UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported): October 20, 2015

PMC-Sierra, Inc.

(Exact Name of Registrant as Specified in its Charter)

1380 Bordeaux Drive

Sunnyvale, CA 94089

(408) 239-8000

(Address of Principal Executive Offices, including zip code)

(408) 239-8000

(Registrant’s telephone number including area code)

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligations of the registrant under any of the following provisions (see General Instruction A.2. below):

On October 20, 2015, PMC-Sierra, Inc. (“PMC”) announced that it had received an unsolicited proposal from Microsemi Corporation (“Microsemi”) to acquire all of the outstanding shares of PMC for $8.75 in cash and 0.0736 of a share of Microsemi common stock for each share of PMC common stock.

A copy of the press release issued by PMC is attached hereto as Exhibit 99.1 and is incorporated by reference herein.

Additional Information and Where You Can Find It

PMC plans to file with the SEC and mail to our stockholders a proxy statement in connection with the proposed Skyworks transaction. Additionally, PMC may file other relevant materials with the SEC in connection with the proposed Skyworks transaction. The proxy statement and other relevant materials will contain important information about PMC, Skyworks, the proposed transaction, and related matters. Investors and security holders are urged to read the proxy statement and the other relevant materials with respect to the proposed merger with Skyworks carefully in their entirety when they become available before making any voting or investment decision with respect to the proposed merger with Skyworks because they will contain important information about the proposed merger and the parties to the merger.

This document does not constitute an offer to sell, or the solicitation of an offer to buy, any securities, or a solicitation of any vote or approval, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. If a negotiated transaction between PMC and Microsemi is agreed, PMC and Microsemi will prepare and file a registration statement that will include a proxy statement/prospectus related to the proposed transaction, the proposed transaction will be submitted to the stockholders of PMC for their consideration, and PMC will provide the proxy statement/prospectus to its stockholders. PMC, and possibly Microsemi, may also file other documents with the SEC regarding the proposed transaction. This document is not a substitute for any prospectus, proxy statement or any other document which PMC or Microsemi may file with the SEC in connection with the proposed transaction. Investors and security holders are urged to read the proxy statement/prospectus and the other relevant materials with respect to the proposed transaction with Microsemi carefully in their entirety when they become available before making any voting or investment decision with respect to the proposed transaction with Microsemi, because they will contain important information about the proposed transaction with Microsemi.

Investors and security holders will be able to obtain free copies of the proxy statement or proxy statement / prospectus, as applicable, and relevant other documents filed with the SEC by PMC, Skyworks and/or Microsemi through the website maintained by the SEC at www.sec.gov.

PMC and its directors and executive officers may be deemed to be participants in the solicitation of proxies in respect of the transactions contemplated by the merger agreement with Skyworks or the proposed transaction with Microsemi. Information regarding PMC’s directors and executive officers and their ownership of PMC’s common stock is contained in PMC’s Form 10-K for the year ended December 27, 2014 and its proxy statement dated March 20, 2015, which are filed with the SEC. Additional information regarding the participants in the solicitation of proxies in respect of the transaction contemplated by the merger agreement, or the transaction contemplated by the Microsemi proposal, as applicable, and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in any registration statement, prospectus, proxy statement and other relevant materials to be filed with the SEC if and when they become available.

The following exhibits are furnished with this Current Report:

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

EXHIBIT INDEX