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

August 12, 2015

Date of Report (Date of earliest event reported)

ON Semiconductor Corporation

(Exact name of registrant as specified in its charter)

(602) 244-6600

(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 obligation of the registrant under any of the following provisions:

On August 12, 2015 and effective as of August 13, 2015, the Board of Directors (“Board”) of ON Semiconductor Corporation (the “Corporation”) elected Gilles Delfassy to serve as a Class II director of the Board. The Board also appointed Mr. Delfassy to its Science & Technology Committee. As a Class II director, Mr. Delfassy’s term will expire at the 2016 annual meeting of stockholders (or at such time as his successor is duly elected and qualified, or the earlier of his resignation or removal). Mr. Delfassy’s continued service on the Board will be voted on by the Corporation’s stockholders at the 2016 annual meeting of stockholders.

In connection with this election, Mr. Delfassy will be eligible under the Corporation’s compensation program for non-employee members of the Board (“Program”). Under this Program, Mr. Delfassy will receive the following compensation for his services:

(1) Board Annual Retainer — Non-employee directors are entitled to an annual cash retainer of $60,000 per year. Annual cash retainers are paid quarterly in arrears, and Mr. Delfassy will receive a pro-rated retainer based upon the period of time that he served on the Board.

(2) Committee Annual Retainer — Under the Program, members of the Science & Technology Committee are entitled to an annual cash retainer in the amount of $5,000 per year. Board committee cash retainers are paid quarterly in arrears, and Mr. Delfassy will receive a pro-rated retainer based upon the period of time that he served on the Science & Technology Committee.

(3) Equity Compensation — Under the Program, our non-employee directors also receive an annual award of fully-vested stock with a value equal to $195,000 at or around the Corporation’s annual meeting of stockholders. Mr. Delfassy will be entitled to a pro rata portion of this grant based upon the time served between August 13, 2015 and the next annual meeting of shareholders. This award is subject to the Corporation’s Amended and Restated Stock Incentive Plan and the relevant award agreement.

(4) Other — Mr. Delfassy will be reimbursed for reasonable expenses to attend Board and committee meetings, as applicable, and to perform other relevant Board duties. Except as described above, Mr. Delfassy will not receive any additional compensation for his service as a member of the Board.

Attached to this Current Report, as Exhibit 99.1, is a copy of the Corporation’s news release dated August 18, 2015 titled “New Member Named to ON Semiconductor’s Board of Directors.”

(a) Financial Statements of Business Acquired

Not applicable.

(b) Pro Forma Financial Information

Not applicable.

(c) Shell Company Transactions

Not applicable.

(d) Exhibits

The below exhibit is furnished as part of this 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