UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 10-K  ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 FOR THE FISCAL YEAR ENDED SEPTEMBER 30, 2012 or □ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 to For the transition period from COMMISSION FILE NUMBER 000-30205 CABOT MICROELECTRONICS CORPORATION (Exact name of registrant as specified in its charter) DELAWARE (State of Incorporation) 36-4324765 (I.R.S. Employer Identification No.) 870 NORTH COMMONS DRIVE 60504 AURORA, ILLINOIS (Zip Code) (Address of principal executive offices) Registrant’s telephone number, including area code: (630) 375-6631 Securities registered pursuant to Section 12(b) of the Act: Title of each class Name of each exchange on which registered Common Stock, $0.001 par value The NASDAQ Stock Market LLC Securities registered pursuant to Section 12(g) of the Act: None Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes  No □ Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes □ No  Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes  No □ Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (Section 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). Yes  No □ Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.  Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See definition of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one): Large accelerated filer  Accelerated filer □ Non-accelerated filer □ Smaller reporting company □ Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes □ No  The aggregate market value of the registrant’s Common Stock held beneficially or of record by stockholders who are not affiliates of the registrant, based upon the closing price of the Common Stock on March 31, 2012, as reported by the NASDAQ Global Select Market, was approximately $892,790,000. For the purposes hereof, “affiliates” include all executive officers and directors of the registrant. As of October 31, 2012, the Company had 23,193,584 shares of Common Stock outstanding. DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive Proxy Statement for the Annual Meeting of Stockholders to be held on March 5, 2013, are incorporated by reference in Part III of this Form 10-K to the extent stated herein. This Form 10-K includes statements that constitute “forward-looking statements” within the meaning of federal securities regulations. For more detail regarding “forward-looking statements” see Item 7 of Part II of this Form 10-K.