Form 424B3 FORMFACTOR INC

SUMMARY

This summary highlights selected information from this proxy statement/prospectus. It may not contain all of the information that is important to you. You are urged to read carefully the entire proxy statement/prospectus and the other documents referred to in this proxy statement/prospectus in their entirety in order to fully understand the merger agreement and the proposed merger. See “Where You Can Find More Information” beginning on page 136 of this proxy statement/prospectus. Each item in this summary refers to the page of this proxy statement/prospectus on which that subject is discussed in more detail.

Information about FormFactor, Cascade Microtech and Cardinal Merger Subsidiary, Inc. (See Page 55)

FormFactor, Inc.

FormFactor, Inc., which is referred to in this proxy statement/prospectus as FormFactor, was incorporated in the State of Delaware in 1993. FormFactor helps semiconductor manufacturers test the integrated circuits that power consumer mobile devices, as well as computing, automotive and other applications. FormFactor is one of the world’s leading providers of essential wafer test technologies and expertise, with an extensive portfolio of high-performance probe cards for DRAM, Flash and System on Chip devices. Customers use FormFactor’s products and services to lower overall production costs, improve their yields and enable complex next-generation integrated circuits. Headquartered in Livermore, California, FormFactor services its customers from a network of facilities in Europe, Asia and North America.

The principal trading market for FormFactor’s common stock (NASDAQ: FORM) is the NASDAQ Global Market. The principal executive offices of FormFactor are located at 7005 Southfront Road, Livermore, California 94551; its telephone number is (925) 290-4000; and its website is www.FormFactor.com. The information and other content contained on its website is not incorporated by reference in this proxy statement/prospectus.

Cascade Microtech, Inc.

Cascade Microtech, Inc., which is referred to in this proxy statement/prospectus as Cascade Microtech, was incorporated in the State of Oregon in 1984. Cascade Microtech is a worldwide leader in precision contact, electrical measurement and test of integrated circuits, optical devices and other small structures. For technology businesses and scientific institutions that need to evaluate small structures, Cascade Microtech delivers access to electrical data from wafers, integrated circuits, integrated circuit packages, circuit boards and modules, MEMS, 3D TSV, LED devices and more. Cascade Microtech’s leading-edge stations, probes, probe cards, advanced thermal subsystems and integrated systems deliver precision accuracy and superior performance both in the lab and during production manufacturing of high-speed and high-density semiconductor chips.

The principal trading market for Cascade Microtech’s common stock (NASDAQ: CSCD) is the NASDAQ Global Market. The principal executive offices of Cascade Microtech are located at 9100 S.W. Gemini Drive, Beaverton, Oregon 97008; its telephone number is (503) 601-1000; and its website is www.cascademicrotech.com. The information and other content contained on its website is not incorporated by reference in this proxy statement/prospectus.

Cardinal Merger Subsidiary, Inc.

Cardinal Merger Subsidiary, Inc., which is referred to in this proxy statement/prospectus as Merger Sub, is an Oregon corporation and a wholly owned subsidiary of FormFactor. Merger Sub was incorporated on February 1, 2016 solely for the purpose of consummating a merger with Cascade Microtech. Merger Sub has not carried on any activities to date, except for activities incidental to its formation and activities undertaken in connection with the merger.

The principal executive offices of Merger Sub are located at 7005 Southfront Road, Livermore, California 94551 and its telephone number is (925) 290-4000.

The Merger (See Page 61).

FormFactor, Merger Sub and Cascade Microtech have entered into the Agreement and Plan of Merger, dated as of February 3, 2016, which, as it may be amended from time to time, is referred to in this proxy statement/prospectus as the merger agreement. Subject to the terms and conditions of the merger agreement and in accordance with Oregon law, Merger Sub will be merged with and into Cascade Microtech, with Cascade Microtech continuing as the surviving corporation. Upon completion of this transaction, which is referred to in this proxy statement/prospectus as the merger, Cascade Microtech will be a wholly owned subsidiary of FormFactor, and Cascade Microtech common stock will no longer be publicly traded.

A copy of the merger agreement is attached as Annex A to this proxy statement/prospectus. You should read the merger agreement carefully because it is the legal document that governs the merger.

Special Meeting of Cascade Microtech’s Shareholders (See Page 56).

Meeting. The special meeting will be held at the offices of Perkins Coie LLP, located at 1120 N.W. Couch Street, Tenth Floor, Portland, Oregon 97209 on June 23, 2016 at 10:00 a.m., local time. At the special meeting, Cascade Microtech shareholders will be asked to vote on the following proposals:

Record Date. Only Cascade Microtech shareholders of record at the close of business on May 5, 2016 will be entitled to receive notice of and to vote at the special meeting or any adjournment of the special meeting. As of the close of business on the record date of May 5, 2016, there were 15,949,492 shares of Cascade Microtech common stock outstanding and entitled to vote at the special meeting. Each holder of Cascade Microtech common stock is entitled to one vote for each share of Cascade Microtech common stock owned as of the record date.

Quorum. A quorum of shareholders is necessary to have a valid meeting of Cascade Microtech shareholders. A majority of the shares of Cascade Microtech common stock issued and outstanding and entitled to vote on the record date must be present in person or by proxy at the Cascade Microtech special meeting in order for a quorum to be established. Abstentions and broker “non-votes” count as present for establishing the quorum described above. A broker may not vote on any of the Cascade Microtech proposals without instructions from the beneficial owner of the shares, and without such instructions a broker “non-vote” will occur.

Required Vote. Approval and adoption of the merger agreement, the merger pursuant to merger agreement and the related transactions contemplated by the merger agreement, requires the affirmative vote of holders of at least a majority of the outstanding shares of Cascade Microtech common stock entitled to vote thereon.

Approval of the adjournment of the special meeting requires the affirmative vote of holders of a majority of the shares of Cascade Microtech common stock present at the special meeting, in person or by proxy, whether or not a quorum.

Approval, on an advisory (non-binding) basis, of the merger-related compensation that will or may be paid to Cascade Microtech’s named executive officers in connection with the merger will occur if the votes cast in favor of the proposal exceed the votes cast against it.

Stock Ownership of and Voting by Cascade Microtech’s Directors and Executive Officers. At the close of business on the record date for the special meeting, Cascade Microtech’s directors and executive officers and their affiliates beneficially owned and had the right to vote an aggregate of 2,120,616 shares of Cascade Microtech common stock at the special meeting, which represents approximately 13.3% of the shares of Cascade Microtech common stock then outstanding and entitled to vote at the special meeting.

It is expected that Cascade Microtech’s directors and executive officers will vote their shares “FOR” the adoption of the merger agreement, although none of them has entered into any agreement requiring them to do so.

What Cascade Microtech’s Shareholders Will Receive in the Merger (See Page 95).

If the merger is consummated, Cascade Microtech’s shareholders will be entitled to receive in the merger, for each share of Cascade Microtech common stock that they own, a combination of $16.00 in cash, without interest (which is referred to in this proxy statement/prospectus as the per share cash consideration), and 0.6534 of a share of FormFactor common stock (which, as adjusted, is referred to in this proxy statement/prospectus as the exchange ratio), in each case subject to adjustment in certain circumstances as described below under the heading “The Merger Agreement—Exchange Ratio Adjustment” beginning on page 95 of this proxy statement/prospectus, which together with cash payable in lieu of any fractional shares as described below are collectively referred to in this proxy statement/prospectus as the merger consideration.

FormFactor will not issue any fractional shares of its common stock in the merger. Instead, the total number of shares of FormFactor common stock that each Cascade Microtech shareholder will receive in the merger will be rounded down to the nearest whole number, and each Cascade Microtech shareholder will receive cash, without interest, for any fractional shares of FormFactor common stock that he or she would otherwise receive in the merger. The amount of cash for fractional shares will be calculated by multiplying the fraction of a share of FormFactor common stock that the Cascade Microtech shareholder would otherwise be entitled to receive in the merger by the volume weighted average price for a share of FormFactor common stock on the NASDAQ Global Market for the ten consecutive trading days ending on the trading day immediately preceding the consummation of the merger, which average is referred to in this proxy statement/prospectus as the FormFactor closing VWAP.

Example: Assuming there has been no adjustment to the exchange ratio, if you currently own 100 shares of Cascade Microtech common stock, you will be entitled to receive $1,600.00 in cash and 65 shares of FormFactor common stock (plus an amount in cash for the market value of 0.34 of a share of FormFactor common stock at the FormFactor closing VWAP) in exchange for your shares, without interest and less any applicable withholding taxes.

The exchange ratio, initially set at 0.6534 of a share of FormFactor common stock for each share of Cascade Microtech common stock, and the related per share cash consideration are only subject to adjustment in the circumstances described below and in “The Merger Agreement—Exchange Ratio Adjustment” beginning on page 95 of this proxy statement/prospectus. Such adjustments, if any, are not designed to preserve the value of the stock portion of the merger consideration if the market price of FormFactor common stock or Cascade Microtech common stock changes between the signing of the merger agreement and the consummation of the merger. The value of the stock portion of the merger consideration will depend on the market price of FormFactor common stock at the time Cascade Microtech’s shareholders receive FormFactor common stock in the merger. Based on the closing stock price of a share of FormFactor common stock of $6.70 on the NASDAQ Global Market on May 17, 2016, the most recent practicable date prior to the date of this proxy statement/prospectus, the value of the merger consideration was $20.38 per share of Cascade Microtech common stock, which includes the value of the stock portion of the merger consideration of $4.38 per share and the cash portion of the merger consideration of $16.00 per share of Cascade Microtech common stock. The market price of

FormFactor common stock will fluctuate prior to the merger, and, when received by Cascade Microtech’s shareholders after the merger is consummated, could be greater, less than or the same as the current market price of FormFactor common stock or the market price at the time of the Cascade Microtech special meeting.

Exchange Ratio Adjustment (See Page 95).

The exchange ratio, initially set at 0.6534 shares of FormFactor common stock for each share of Cascade Microtech common stock, is subject to adjustment if the number of shares of FormFactor common stock that would be issued to Cascade Microtech common shareholders as part of the merger consideration plus the number of shares that would be subject to assumed equity awards upon consummation of the merger would, in the aggregate, exceed 19.9% of the issued and outstanding shares of FormFactor common stock immediately prior to the consummation of the merger. In such event, the exchange ratio will be reduced to the minimum extent necessary such that the aggregate number of shares issued in the merger or made subject to assumed equity awards using the adjusted exchange ratio would equal 19.9% of the issued and outstanding shares of FormFactor common stock immediately prior to the consummation of the merger. If this adjustment occurs, shareholders of Cascade Microtech common stock will receive an increase in the amount of cash they receive as part of the merger consideration per share equal to the amount by which the exchange ratio is reduced multiplied by the FormFactor closing VWAP. In no event will the exchange ratio be increased above 0.6534 shares of FormFactor common stock, nor will the per share cash consideration be reduced below $16.00, in connection with an adjustment described in this paragraph. See “The Merger Agreement—Exchange Ratio Adjustment” beginning on page 95 of this proxy statement/prospectus for a discussion of the factors that influence whether there will be an adjustment to the exchange ratio and the degree of any such adjustment, and the impact under certain illustrative scenarios of various changes to those factors.

The exchange ratio and per share cash consideration are also subject to customary adjustments in the event of a recapitalization, stock split or combination, stock dividend or similar change to the capital stock of FormFactor or Cascade Microtech between the date of the merger agreement and the consummation of the merger.

Treatment of Equity Awards (See Page 98).

Upon consummation of the merger:

Recommendation of the Cascade Microtech Board of Directors (See Page 69).

Cascade Microtech’s board of directors unanimously determined that the merger agreement, the merger and the related transactions contemplated by the merger agreement are advisable for, fair to and in the best interests of Cascade Microtech and its shareholders and unanimously approved the merger agreement, the merger and the transactions contemplated thereby. The Cascade Microtech board of directors unanimously recommends that Cascade Microtech’s shareholders vote “FOR” approval and adoption of the merger agreement, the merger and the related transactions contemplated by the merger agreement. For a description of factors considered by the Cascade Microtech board of directors in reaching its decision to approve and adopt the merger agreement, the merger pursuant to merger agreement and the related transactions contemplated by the merger agreement, see “Proposal I: The Merger—Cascade Microtech Reasons for the Merger; Recommendation of Cascade Microtech’s Board of Directors” beginning on page 69 of this proxy statement/prospectus.

The Cascade Microtech board of directors unanimously recommends that Cascade Microtech’s shareholders vote “FOR” the Cascade Microtech proposal to adjourn the special meeting, if necessary to solicit additional proxies if there are not sufficient votes to approve and adopt the merger agreement, the merger pursuant to merger agreement and the related transactions contemplated by the merger agreement at the time of the special meeting. See “Proposal II: Adjournment of the Cascade Microtech Special Meeting” beginning on page 125 of this proxy statement/prospectus.

The Cascade Microtech board of directors unanimously recommends that Cascade Microtech shareholders vote “FOR” the proposal to approve, on an advisory (non-binding) basis, the named executive officer merger-related compensation payments that will or may be paid by Cascade Microtech to its named executive officers in connection with the merger. See “Proposal III: Advisory Vote On Named Executive Officer Merger-Related Compensation” beginning on page  126 of this proxy statement/prospectus.

Opinion of Cascade Microtech’s Financial Advisor (See Page 77).

On February 3, 2016, Stifel, Nicolaus & Company, Incorporated, which is referred to in this proxy statement/prospectus as Stifel, Cascade Microtech’s financial advisor, rendered an opinion to Cascade Microtech’s board of directors that, based upon and subject to the procedures followed, assumptions made, qualifications, and limitations on the review undertaken and other matters contained in such opinion, the merger consideration of (i) $16.00 in cash, and (ii) 0.6534 shares of FormFactor’s common stock, subject to adjustment and on terms and conditions more fully set forth in the merger agreement, to be received by Cascade Microtech’s shareholders in the merger pursuant to the terms of the merger agreement was fair, from a financial point of view, to such holders of Cascade Microtech common stock, as of such date. The full text of Stifel’s written opinion is attached as Annex B to this proxy statement/prospectus. You should read the entire opinion for a discussion of, among other things, the assumptions made, procedures followed, matters considered and limitations on the review undertaken by Stifel in rendering its opinion. Stifel provided its opinion to Cascade Microtech’s board of directors (in its capacity as such) for the information and assistance of Cascade Microtech’s board of directors in connection with its consideration of the financial terms of the merger. Stifel’s opinion does not constitute a recommendation to Cascade Microtech’s board of directors as to how the board should vote on the merger agreement, the merger or the related transactions contemplated by the merger agreement or to any shareholder of Cascade Microtech as to how any such

shareholder should vote at Cascade Microtech’s special meeting of shareholders or any other shareholders’ meeting at which the merger is considered. In addition, Stifel’s opinion does not compare the relative merits of the merger with any other alternative transactions or business strategies which may have been available to Cascade Microtech and does not address the underlying business decision of Cascade Microtech’s board of directors or Cascade Microtech to proceed with or effect the merger. See “Proposal I: The Merger—Opinion of Cascade Microtech’s Financial Advisor” beginning on page 77 for additional information.

Ownership of FormFactor After the Merger (See Page 61).

Based on the number of shares of Cascade Microtech common stock outstanding as of May 17, 2016, FormFactor expects to issue approximately 10,438,799 shares of its common stock to Cascade Microtech’s shareholders pursuant to the merger. The actual number of shares of FormFactor common stock to be issued and reserved for issuance pursuant to the merger will be determined at the consummation of the merger based on the exchange ratio of 0.6534, subject to adjustment in certain circumstances as described below under the heading “The Merger Agreement—Exchange Ratio Adjustment” beginning on page 95 of this proxy statement/prospectus, and the number of shares of Cascade Microtech common stock outstanding at such time. Immediately after consummation of the merger, it is expected that former Cascade Microtech’s shareholders will own approximately 14.9% of the outstanding FormFactor common stock, based on the number of shares of Cascade Microtech and FormFactor common stock outstanding, as of May 17, 2016.

FormFactor Shareholder Approval Is Not Required.

FormFactor shareholders are not required to approve and adopt the merger agreement, the merger pursuant to merger agreement or the related transactions contemplated by the merger agreement or approve the issuance of the shares of FormFactor common stock in connection with the merger.

Interests of Certain Persons in the Merger (See Page 120).

In considering the recommendation of the Cascade Microtech board of directors with respect to the merger agreement, Cascade Microtech’s shareholders should be aware that Cascade Microtech’s directors and executive officers have interests in the merger that may be different from, or in addition to, Cascade Microtech’s shareholders generally. The Cascade Microtech board of directors was aware of and considered these interests, among other matters, in evaluating and negotiating the merger agreement and in recommending to Cascade Microtech’s shareholders that the merger agreement be approved.

These interests and arrangements include:

Listing of FormFactor Common Stock and Delisting and Deregistration of Cascade Microtech Common Stock (See Page 91).

FormFactor will apply to have the shares of its common stock to be issued in the merger approved for listing on the NASDAQ Global Market, where FormFactor common stock currently is traded. If the merger is consummated, Cascade Microtech shares will no longer be listed on the NASDAQ Global Market, and will be deregistered under the Securities Exchange Act of 1934, as amended, which is referred to in this proxy statement/prospectus as the Exchange Act.

No Dissenters’ or Appraisal Rights (See Page 89)

Under Oregon law, Cascade Microtech shareholders are not entitled to dissenters’ or appraisal rights in connection with any matters to be considered at the Cascade Microtech special meeting. See “Proposal I: The Merger—No Dissenters’ or Appraisal Rights” beginning on page 89 of this proxy statement/prospectus.

Consummation of the Merger Is Subject to Certain Conditions (See Page 100).

The obligations of each of FormFactor, Cascade Microtech and Merger Sub to consummate the merger is subject to the satisfaction (or, to the extent permitted by applicable law, waiver) of a number of conditions, including the following:

In addition, the obligations of FormFactor and Merger Sub to consummate the merger are subject to the satisfaction (or, to the extent permitted by applicable law, waiver) of the following conditions:

In addition, the obligations of Cascade Microtech to consummate the merger are subject to the satisfaction (or, to the extent permitted by applicable law, waiver) of the following conditions:

FormFactor and Cascade Microtech cannot be certain when, or if, the conditions to the merger will be satisfied or waived, or that the merger will be consummated.

The Merger May Not Be Consummated Without All Required Regulatory Approvals (See Page 88).

As mentioned above, consummation of the merger is conditioned upon the expiration or early termination of the waiting period relating to the merger under the HSR Act. FormFactor and Cascade Microtech each filed its required HSR notification and report form with respect to the merger on February 18, 2016. The waiting period relating to the merger under the HSR Act expired on March 21, 2016. FormFactor and Cascade Microtech have agreed to use their respective reasonable best efforts to take all actions required to consummate the merger, including effecting all necessary filings, notices, petitions and other documents and obtaining and maintaining all approvals, consents, authorizations and other confirmations required to be obtained from any governmental authority or other third party, except that neither party is required under the merger agreement to enter into a settlement, consent decree or other agreement with a governmental authority in connection with the merger or divest, hold separate or take any other action with respect to any of its or the surviving corporation’s subsidiaries or any portion of their respective affiliate’s businesses, assets or properties.

Financing (See Page 92).

The merger agreement is not subject to a financing condition. On February 3, 2016, FormFactor entered into a debt commitment letter pursuant to which HSBC Bank USA, National Association, MUFG Union Bank, N.A., Comerica Bank, and Silicon Valley Bank, which are referred to in this proxy statement/prospectus as the lenders,

have committed to provide a senior secured term loan facility in an aggregate amount of $150 million, which is referred to in this proxy statement/prospectus as the term loan facility, to finance in part, the cash consideration for the merger, which is referred to in this proxy statement/prospectus as the financing. The lenders’ commitment to provide the term loan facility is subject to certain conditions, including, among others, the execution of definitive financing documentation, the consummation of the merger in accordance with the merger agreement substantially simultaneously with the initial funding of the term loan facility, the absence of a company material adverse effect (see “The Merger Agreement— Definition of Company Material Adverse Effect” beginning on page 102 of this proxy statement/prospectus for a definition of “company material adverse effect”), a minimum liquidity condition, the delivery to the lenders of certain financial statements and forecasts, perfection of security interests and other customary closing conditions as fully set forth in the commitment letter. For a more complete description of FormFactor’s debt financing for the merger, see “Proposal I: The Merger—Description of Debt Financing” beginning on page 92 of this proxy statement/prospectus.

The Merger Is Expected to Occur in Mid-2016 (See Page 95).

The merger will occur within two business days after the conditions to its completion have been satisfied or, to the extent legally permissible, waived, unless otherwise mutually agreed upon by the parties. As of the date of this proxy statement/prospectus, the merger is expected to occur in mid-2016. However, there can be no assurance as to when, or if, the merger will occur.

No Solicitation by Cascade Microtech (See Page 106).

The merger agreement provides that neither Cascade Microtech nor any of its subsidiaries will, and Cascade Microtech and its subsidiaries’ will not permit or authorize their officers, directors, employees and other representatives to, (i) solicit, initiate or take any action to facilitate or encourage the submission of any competing acquisition proposal from any third party relating to an acquisition of Cascade Microtech (see “The Merger Agreement—No Solicitation by Cascade Microtech” beginning on page 106 of this proxy statement/prospectus for a definition of “acquisition proposal”), (ii) enter into or participate in any discussions or negotiations regarding any such proposal or furnish any information relating to Cascade Microtech or its subsidiaries to any third party that has made or is seeking to make any such proposal, (iii) fail to make, withdraw or modify in a manner adverse to FormFactor the recommendation of the Cascade Microtech board of directors in favor of the adoption of the merger agreement, recommend for or fail to recommend against any competing acquisition proposal from any third party relating to an acquisition of Cascade Microtech within five business days after such competing acquisition proposal is made public, make any public statement inconsistent with the board recommendation, or publicly propose to do any of the foregoing (any of these activities in this clause (iii) are referred to in this proxy statement/prospectus as an adverse recommendation change ), (iv) fail to enforce or grant any waiver or release under a standstill or similar agreement with respect to any equity securities of Cascade Microtech or its subsidiaries, (v) approve any transaction, or any person becoming an “interested shareholder” under, the Oregon Revised Statutes, Sections 60.825 to 60.845 or cause the Oregon Control Share Act to become applicable to the merger or the transactions contemplated by the merger agreement or (vi) enter into an agreement, letter of intent or similar instrument relating to a competing acquisition proposal. However, the merger agreement provides that, notwithstanding these restrictions and under specified circumstances at any time prior to the adoption of the merger agreement by Cascade Microtech’s shareholders:

Prior to taking the actions described in the above bullets Cascade Microtech is required by the merger agreement to deliver a written notice to FormFactor and, after taking such actions, must continue to advise FormFactor on a current basis of the status and material terms of any discussions with a third party or, after a competing acquisition proposal is made, the status and material details of such competing acquisition proposal.

Termination of the Merger Agreement (See Page 115).

The merger agreement may be terminated at any time before the consummation of the merger by mutual written consent of FormFactor and Cascade Microtech.

The merger agreement may also be terminated by either FormFactor or Cascade Microtech prior to the consummation of the merger if:

The merger agreement may also be terminated by FormFactor prior to the consummation of the merger if:

The merger agreement may also be terminated prior to the consummation of the merger by Cascade Microtech if:

Under the merger agreement, the making of an adverse recommendation change by the Cascade Microtech board of directors in response to any event other than a superior proposal will not give Cascade Microtech the right to terminate the merger agreement, and, in such case, unless FormFactor terminates the merger agreement or Cascade Microtech has the right to terminate the merger agreement on other grounds, Cascade Microtech would remain obligated to call and hold a special meeting of its shareholders for purposes of voting on a proposal to approve and adopt the merger agreement, the merger pursuant to merger agreement and the related transactions contemplated by the merger agreement.

Termination Fees and Expenses (See Page 117).

Cascade Microtech has agreed to pay a fee of $10,830,000 to FormFactor if the merger agreement is terminated:

FormFactor has agreed to pay a fee of $16,245,000 to Cascade Microtech if the merger agreement is terminated by either FormFactor or Cascade Microtech due to the failure of the merger to be consummated prior to the end date and all conditions to closing have been satisfied or waived other than one or more of the “regulatory conditions” relating to the absence of clearance of the merger under the HSR Act (which clearance was obtained through the expiration of the HSR Act waiting period on March 21, 2016) and as defined in “The Merger Agreement—Termination of the Merger Agreement” beginning on page 115 of this proxy statement/prospectus, except in the case where (x) the failure of any of these regulatory conditions was caused by an intentional and material breach by Cascade Microtech of its obligations with respect to such matters or (y) FormFactor has provided Cascade Microtech with a notice of its intention to extend the end date beyond August 4, 2016 and Cascade Microtech fails to provide its written consent accepting the extension by the second business day after receiving the notice. See “The Merger Agreement—Termination of the Merger Agreement” beginning on page 115 of this proxy statement/prospectus. Because the waiting period under the HSR Act relating to the merger expired on March 21, 2016, FormFactor will not be required to pay a termination fee to Cascade Microtech.

If either party pays the termination fee as described above, then, except in the case of fraud, the termination fee will constitute the other party’s sole and exclusive remedy against the paying party and its affiliates, other than any injunctive relief otherwise provided for in the merger agreement.

See “The Merger Agreement—Termination Fee and Expenses” beginning on page 117 of this proxy statement/prospectus for a more complete description of the circumstances under which FormFactor or Cascade Microtech will be required to pay a termination fee.

Specific Performance; Remedies (See Page 119).

Under the merger agreement, each of FormFactor and Cascade Microtech is entitled to seek an injunction to prevent breaches of the merger agreement or to enforce specifically the terms and provisions of the merger agreement, in addition to any other remedy to which that party may be entitled to at law or in equity.

Material U.S. Federal Income Tax Consequences (See Page 89).

In general, U.S. Holders (as defined under “Proposal I: The Merger—Material U.S. Federal Income Tax Consequences”) will recognize capital gain or loss for U.S. federal income tax purposes on the exchange of their Cascade Microtech common stock for shares of FormFactor common stock and cash in an amount equal to the difference, if any, between (i) the sum of the fair market value of the FormFactor common stock on the date of the exchange and the amount of cash received (including cash received in lieu of a fractional share of FormFactor common stock) and (ii) the U.S. Holder’s adjusted tax basis in the Cascade Microtech common stock surrendered in the exchange.

The U.S. federal income tax consequences described above may not apply to all holders of Cascade Microtech common stock, including certain holders specifically referred to on page 89 of this proxy statement/prospectus. Your tax consequences will depend on your own situation. You should consult your tax advisor to determine the particular tax consequences of the merger to you.

Accounting Treatment (See Page 91).

In accordance with accounting principles generally accepted in the United States, which are referred to in this proxy statement/prospectus as GAAP, FormFactor will account for the merger as an acquisition of a business.

Rights of Cascade Microtech’s Shareholders Will Change as a Result of the Merger (See Page 130).

Cascade Microtech’s shareholders will have different rights once they become FormFactor stockholders due to differences in applicable law and differences between the organizational documents of FormFactor and Cascade Microtech. These differences are described in more detail under “Comparison of Shareholder Rights” beginning on page 130 of this proxy statement/prospectus.

Litigation Relating to the Merger (See Page 91).

Two putative class actions have been filed against Cascade Microtech, its directors, FormFactor, and Merger Sub in connection with Cascade Microtech entering into the merger agreement. See “Proposal I: The Merger—Litigation Relating to the Merger” beginning on page 91 of this proxy statement/prospectus.

SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA OF FORMFACTOR

The following consolidated statement of operations data of FormFactor for each of the years ended December 26, 2015, December 27, 2014 and December 28, 2013 and consolidated balance sheet data of FormFactor as of December 26, 2015 and December 27, 2014 has been derived from FormFactor’s audited consolidated financial statements and related notes contained in its Annual Report on Form 10-K for the year ended December 26, 2015, which is incorporated by reference in this proxy statement/prospectus. The consolidated statement of operations data of FormFactor for each of the years ended December 29, 2012 and December 31, 2011 and consolidated balance sheet data of FormFactor as of December 28, 2013, December 29, 2012 and December 31, 2011 have been derived from FormFactor’s audited consolidated financial statements for such years, which have not been incorporated in this proxy statement/prospectus by reference. The unaudited consolidated statement of operations data of FormFactor for the three months ended March 26, 2016 and March 28, 2015 and unaudited consolidated balance sheet data as of March 26, 2016 and March 28, 2015 are derived from FormFactor’s unaudited condensed consolidated financial statements and related notes contained in its Quarterly Report on Form 10-Q for the quarter ended March 26, 2016, which is incorporated by reference into this proxy statement/prospectus. FormFactor’s management believes that its unaudited condensed consolidated financial data have been prepared on a basis consistent with its audited financial statements and include all normal and recurring adjustments necessary for a fair presentation of the results for each interim period. Results for past periods are not necessarily indicative of results that may be expected for fiscal year 2016 or for any other period.

SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA OF CASCADE MICROTECH

The following consolidated statement of operations data of Cascade Microtech for each of the years ended December 31, 2015, 2014 and 2013 and consolidated balance sheet data of Cascade Microtech as of December 31, 2015 and 2014 has been derived from Cascade Microtech’s audited consolidated financial statements and related notes contained in its Annual Report on Form 10-K for the year ended December 31, 2015, which is incorporated by reference in this proxy statement/prospectus. The consolidated statement of operations data of Cascade Microtech for each of the years ended December 31, 2012 and 2011 and consolidated balance sheet data of Cascade Microtech as of December 31, 2013, 2012 and 2011 have been derived from Cascade Microtech’s audited consolidated financial statements for such years, which have not been incorporated in this proxy statement/prospectus by reference. The unaudited consolidated statement of operations data of Cascade Microtech for the three months ended, March 31, 2016 and 2015 and unaudited consolidated balance sheet data as of March 31, 2016 and 2015, are derived from Cascade Microtech’s unaudited condensed consolidated financial statements and related notes contained in its Quarterly Report on Form 10-Q for the quarter ended March 31, 2016, which is incorporated by reference into this proxy statement/prospectus. Cascade Microtech’s management believes that its unaudited condensed consolidated financial data have been prepared on a basis consistent with its audited financial statements and include all normal and recurring adjustments necessary for a fair presentation of the results for each interim period. Results for past periods are not necessarily indicative of results that may be expected for fiscal year 2016 or for any other period.

COMPARATIVE HISTORICAL AND UNAUDITED PRO FORMA PER SHARE DATA

The following table sets forth selected historical and unaudited pro forma combined per share information for FormFactor and Cascade Microtech.

Historical Per Share Information of FormFactor and Cascade Microtech. The historical per share information of each of FormFactor and Cascade Microtech below is derived from the audited consolidated financial statements of FormFactor as of and for the year ended, December 26, 2015 and Cascade Microtech as of and for the year ended, December 31, 2015 and the unaudited condensed consolidated financial statements of FormFactor as of and for the three months ended March 26, 2016 and Cascade Microtech as of and for the three months ended March 31, 2016.

Unaudited Pro Forma Combined FormFactor Common Share Data. The unaudited pro forma combined FormFactor common share data set forth below gives effect to the merger under the acquisition method of accounting, as if the merger had been effective on December 28, 2014, the first day of FormFactor’s fiscal year ended December 26, 2015, in the case of income (loss) from operations and cash dividends data and at March 26, 2016, in the case of book value per share data, and assuming that each outstanding share of Cascade Microtech common stock had been converted into shares of FormFactor common stock based on the exchange ratio (0.6534 of a share of FormFactor common stock for each share of Cascade Microtech common stock, assuming no adjustments). The exchange ratio does not include the cash portion of the merger consideration.

The unaudited pro forma combined FormFactor common share data is derived from the audited consolidated financial statements of FormFactor as of and for the year ended, December 26, 2015 and Cascade Microtech as of and for the year ended December 31, 2015 and the unaudited condensed consolidated financial statements of FormFactor as of and for the three months ended March 26, 2016 and Cascade Microtech as of and for the three months ended March 31, 2016.

The acquisition method of accounting is based on Financial Accounting Standards Board, Accounting Standards Codification (which is referred to in this proxy statement/prospectus as ASC) 805, Business Combinations, and uses the fair value concepts defined in ASC 820, Fair Value Measurements and Disclosures, which FormFactor has adopted as required. Acquisition accounting requires, among other things, that most assets acquired and liabilities assumed be recognized at their fair values as of the acquisition date. The acquisition accounting is dependent upon certain valuations of Cascade Microtech’s assets and liabilities and other studies that have yet to commence or progress to a stage where there is sufficient information for a definitive measurement. Accordingly, the pro forma adjustments reflect the assets and liabilities of Cascade Microtech at their preliminary estimated fair values. Differences between these preliminary estimates and the final acquisition accounting will occur, and these differences could have a material impact on the unaudited pro forma combined per share information set forth in the following table.

The unaudited pro forma condensed combined financial information has been presented for informational purposes only. The unaudited pro forma combined FormFactor common share data does not purport to represent the actual results of operations that FormFactor would have achieved had the companies been combined during the given period or to project the future results of operations that FormFactor may achieve after the merger. The unaudited pro forma condensed combined financial information does not reflect the realization of any cost savings following consummation of the merger and also does not reflect any related restructuring and integration charges to achieve those cost savings.

Unaudited Pro Forma Combined Cascade Microtech Equivalent Share Data. The unaudited pro forma combined Cascade Microtech equivalent share data set forth below shows the effect of the merger from the

perspective of an owner of Cascade Microtech common stock. The information was calculated by multiplying the unaudited pro forma combined FormFactor common share amounts by the exchange ratio of 0.6534 (assuming no adjustments).

You should read the below information in conjunction with the selected historical consolidated financial information included elsewhere in this proxy statement/prospectus and the historical consolidated financial statements of FormFactor and Cascade Microtech and related notes that have been filed with the SEC certain of which are incorporated by reference into this proxy statement/prospectus. See “Selected Historical Consolidated Financial Data of FormFactor,” “Selected Historical Consolidated Financial Data of Cascade Microtech” and “Where You Can Find More Information” beginning on pages 21, 23 and 136, respectively, of this proxy statement/prospectus. The unaudited pro forma combined FormFactor common share data and the unaudited pro forma combined Cascade Microtech equivalent share data is derived from, and should be read in conjunction with, the FormFactor and Cascade Microtech unaudited pro forma condensed combined financial statements and related notes included in this proxy statement/prospectus. See “Unaudited Pro Forma Condensed Combined Financial Statements” beginning on page 29 of this proxy statement/prospectus.

COMPARATIVE PER SHARE MARKET PRICE AND DIVIDEND INFORMATION

Market Prices

The following table sets forth, for the fiscal periods indicated, the high and low sales prices per share for FormFactor common stock and Cascade Microtech common stock as reported on the NASDAQ Global Market, which is the principal trading market for both FormFactor common stock, which is listed under the symbol “FORM,” and Cascade Microtech common stock, which is listed under the symbol “CSCD.”

The following table sets forth the closing sale price per share of FormFactor and Cascade Microtech common stock as reported on the NASDAQ Global Market as of February 3, 2016, the last trading day before the public announcement of the merger agreement, and as of May 17, 2016, the most recent practicable trading day prior to the date of this proxy statement/prospectus. The table also shows the implied value of the merger consideration proposed for each share of Cascade Microtech common stock as of the same two dates. This implied value was calculated by multiplying the closing sale price of FormFactor common stock on the relevant date by the exchange ratio of 0.6534 (assuming no adjustments) and adding the cash portion of the merger consideration, or $16.00 (assuming no adjustments).

The market prices of FormFactor and Cascade Microtech common stock may fluctuate between the date of this proxy statement/prospectus and the consummation of the merger. No assurance can be given concerning the market prices of FormFactor or Cascade Microtech common stock before the consummation of the merger or

FormFactor common stock after the consummation of the merger. Because the exchange ratio is only subject to adjustment in circumstances which are not designed to preserve the value of the stock portion of the merger consideration if the market price of FormFactor common stock or Cascade Microtech common stock changes between the signing of the merger agreement and the completion of the merger, the market value of the FormFactor common stock that Cascade Microtech’s shareholders will receive in connection with the merger may vary significantly from the prices shown in the table above. See “Unaudited Pro Forma Condensed Combined Financial Statements—Note 2. Estimated Cascade Microtech Purchase Consideration and Preliminary Purchase Price Allocation” beginning on page 36 of this proxy statement/prospectus and “The Merger Agreement—Exchange Ratio Adjustment” beginning on page 95 of this proxy statement/prospectus. Accordingly, Cascade Microtech’s shareholders are advised to obtain current market quotations for FormFactor and Cascade Microtech common stock in deciding whether to vote for adoption of the merger agreement.

Dividends

Neither FormFactor nor Cascade Microtech have ever declared or paid cash dividends on its common stock and each expects to retain all available funds and any future earnings for use in the operation and development of its respective business. Accordingly, neither FormFactor nor Cascade Microtech anticipate declaring or paying cash dividends on its common stock in the foreseeable future.

UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION

Introduction

The following unaudited pro forma condensed combined financial information is presented to illustrate the estimated effects of the pending merger of Merger Sub with and into Cascade Microtech, with Cascade Microtech continuing as the surviving corporation and as a wholly owned subsidiary of FormFactor and the related financing transactions, which were announced on February 4, 2016.

The merger has not yet closed. Under the terms of the merger agreement, FormFactor is offering to acquire each outstanding share of common stock of Cascade Microtech common stock (other than any shares held by any subsidiary of Cascade Microtech or FormFactor, which will be converted into shares of the surviving corporation) in exchange for $16.00 in cash and 0.6534 of a share of FormFactor common stock, which is referred to in this proxy statement/prospectus as the merger consideration.

Pro Forma Information

The unaudited pro forma condensed combined statements of operations for the three months ended March 26, 2016 and year ended December 26, 2015 combine the historical consolidated statements of operations of FormFactor for the quarter ended March 26, 2016 and for the fiscal year ended December 26, 2015 respectively, and Cascade Microtech for the quarter ended March 31, 2016 and for the fiscal year ended December 31, 2015. The unaudited pro forma condensed combined balance sheet as of March 26, 2016 combines the historical consolidated balance sheet of FormFactor as of March 26, 2016 with Cascade Microtech as of March 31, 2016, giving effect to the merger as if it had occurred on March 26, 2016. The historical consolidated financial information has been adjusted in the unaudited pro forma condensed combined financial information to give effect to pro forma events that are (i) directly attributable to the merger, (ii) factually supportable and (iii) with respect to the statements of operations, expected to have a continuing impact on the combined results. The unaudited pro forma condensed combined financial information has been prepared by FormFactor using the acquisition method of accounting in accordance with GAAP.

The unaudited pro forma condensed combined financial information should be read in conjunction with the accompanying notes to the unaudited pro forma condensed combined financial information. In addition, the unaudited pro forma condensed combined financial information is based on and should be read in conjunction with the following historical consolidated financial statements and accompanying notes, which are incorporated by reference in this proxy statement/prospectus:

The unaudited pro forma condensed combined financial information reflects the estimated aggregate consideration of approximately $350.8 million for the acquisition, as calculated below (in thousands, except number of shares and price per share):

In accordance with the acquisition method of accounting, the actual consolidated financial statements of FormFactor will reflect the Cascade Microtech acquisition only from and after the date of the completion of the acquisition. FormFactor has performed a preliminary valuation analysis of the fair value of Cascade Microtech’s assets to be acquired and liabilities to be assumed. The assets and liabilities of Cascade Microtech have been measured based on various preliminary estimates using assumptions that FormFactor believes are reasonable based on information that is currently available. Differences between these preliminary estimates and the final acquisition accounting will occur, and those differences could have a material impact on the accompanying unaudited pro forma condensed combined financial information and the combined company’s future results of operations and financial position. The pro forma adjustments are preliminary and have been made solely for the purpose of providing unaudited pro forma condensed combined financial statements prepared in accordance with the rules and regulations of the SEC.

FormFactor intends to commence the necessary valuation and other studies required to complete the acquisition accounting promptly upon consummation of the merger and will finalize the acquisition accounting as soon as practicable within the required measurement period in accordance with Accounting Standards Codification (“ASC”) Topic 805, but in no event later than one year following consummation of the merger.

The unaudited pro forma condensed combined financial information has been presented for informational purposes only. The unaudited pro forma condensed combined financial information does not purport to represent the actual results of operations that FormFactor and Cascade Microtech would have achieved had the companies been combined during these periods and is not intended to project the future results of operations that the combined company may achieve after the merger. The unaudited pro forma condensed combined financial information does not reflect the realization of any cost savings following consummation of the merger and also does not reflect any related restructuring and integration charges to achieve those cost savings.

Unaudited Pro Forma Condensed Combined Balance Sheet

As of March 26, 2016

(in thousands)

Unaudited Pro Forma Condensed Combined Statement of Operations

For the three months ended March 26, 2016

(in thousands, except per share amounts)