UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

Date: July 29, 2014

Commission File Number: 1-15060

UBS AG

(Registrant’s Name)

Bahnhofstrasse 45, Zurich, Switzerland, and

Aeschenvorstadt 1, Basel, Switzerland

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F  x             Form 40-F  ¨

UBS AG (“UBS”) produces regular quarterly reports, which are submitted to the SEC under Form 6-K. These reports are prepared in accordance with International Financial Reporting Standards (IFRS). SEC regulations require certain additional disclosures to be included in registration statements relating to offerings of securities. Certain of this additional disclosure follows herein, and should be read in conjunction with UBS’ annual report on Form 20-F for the year ended 31 December 2013, filed with the SEC on 14 March 2014, as well as UBS’s first quarter 2014 report and second quarter report, submitted to the SEC on Forms 6-K on 6 May 2014 and 29 July 2014, respectively.

Capitalization of UBS

The following table presents the consolidated capitalization of UBS in accordance with International Financial Reporting Standards (IFRS) and translated into US dollars.

Capitalization of UBS

Swiss franc (CHF) amounts as of 30 June 2014 have been translated into U.S. dollars (USD) at the rate of CHF 1 = USD 1.12768 (the exchange rate in effect as of 30 June 2014), and CHF amounts as of 31 March 2014 have been translated into U.S. dollars (USD) at the rate of CHF 1 = USD 1.13125 (the exchange rate in effect as of 31 March 2014).

Ratio of Earnings to Fixed Charges

The following table sets forth UBS’s ratio of earnings to fixed charges on an IFRS basis for the periods indicated. The ratios are calculated based on earnings from continuing operations. Ratios of earnings to fixed charges and preferred share dividends are not presented as there were no mandatory preferred share dividends in any of the periods indicated.

This Form 6-K is hereby incorporated by reference into (1) each of the registration statements of UBS AG on Form F-3 (Registration Number 333-178960) and Form S-8 (Registration Numbers 333-49210; 333-49212; 333-127183; 333-127184; 333-162798; 333-162799; 333-162800; 333-178539; 333-178540; 333-178541; and 333-178543) and into each prospectus outstanding under any of the foregoing registration statements, (2) any outstanding offering circular or similar document issued or authorized by UBS AG that incorporates by reference any Form 6-K’s of UBS AG that are incorporated into its registration statements filed with the SEC, and (3) the base prospectus of Corporate Asset Backed Corporation (“CABCO”) dated June 23, 2004 (Registration Number 333-111572), the Form 8-K of CABCO filed and dated June 23, 2004 (SEC File Number 001-13444), and the Prospectus Supplements relating to the CABCO Series 2004-101 Trust dated May 10, 2004 and May 17, 2004 (Registration Number 033-91744 and 033-91744-05).

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, thereunto duly authorized.

Date: July 29, 2014