SAVINGS PLAN	12 Months Ended
Sep. 30, 2012
SAVINGS PLAN [Abstract]
SAVINGS PLAN	12. SAVINGS PLAN Effective in May 2000, we adopted the Cabot Microelectronics Corporation 401(k) Plan (the “401(k) Plan”), which is a qualified defined contribution plan, covering all eligible U.S. employees meeting certain minimum age and eligibility requirements, as defined by the 401(k) Plan. Participants may make elective contributions of up to 60% of their eligible compensation. All amounts contributed by participants and earnings on these contributions are fully vested at all times. The 401(k) Plan provides for matching and fixed non-elective contributions by the Company. Under the 401(k) Plan, the Company will match 100% of the first four percent of the participant’s eligible compensation and 50% of the next two percent of the participant’s eligible compensation that is contributed, subject to limitations required by government regulations. Under the 401(k) Plan, all U.S. employees, even those who do not contribute to the 401(k) Plan, receive a contribution by the Company in an amount equal to four percent of eligible compensation, and thus are participants in the 401(k) Plan. Participants are 100% vested in all Company contributions at all times. The Company’s expense for the 401(k) Plan totaled $4,210, $4,201 and $2,981 for the fiscal years ended September 30, 2012, 2011 and 2010, respectively.

SAVINGS PLAN

12 Months Ended

Sep. 30, 2012

12. SAVINGS PLAN

Effective in May 2000, we adopted the Cabot Microelectronics Corporation 401(k) Plan (the “401(k) Plan”), which is a qualified defined contribution plan, covering all eligible U.S. employees meeting certain minimum age and eligibility requirements, as defined by the 401(k) Plan. Participants may make elective contributions of up to 60% of their eligible compensation. All amounts contributed by participants and earnings on these contributions are fully vested at all times. The 401(k) Plan provides for matching and fixed non-elective contributions by the Company. Under the 401(k) Plan, the Company will match 100% of the first four percent of the participant’s eligible compensation and 50% of the next two percent of the participant’s eligible compensation that is contributed, subject to limitations required by government regulations. Under the 401(k) Plan, all U.S. employees, even those who do not contribute to the 401(k) Plan, receive a contribution by the Company in an amount equal to four percent of eligible compensation, and thus are participants in the 401(k) Plan. Participants are 100% vested in all Company contributions at all times. The Company’s expense for the 401(k) Plan totaled $4,210, $4,201 and $2,981 for the fiscal years ended September 30, 2012, 2011 and 2010, respectively.