On September 10, 2009, Entegris, Inc. (the "Company") entered into an Underwriting Agreement (the "Underwriting Agreement") with Citigroup Global Markets Inc., Goldman, Sachs & Co. and certain other underwriters party thereto (collectively, the "Underwriters"), for the sale of 14,000,000 shares of the Company's common stock at a price to the public of $3.80 per share pursuant to a registration statement on Form S-3 (File No. 333-160212). In addition, the Underwriters have an option to purchase up to an additional 2,100,000 shares of the Company's common stock on the same terms for 30 days from the date of the Underwriting Agreement, solely to cover over-allotments. The Underwriters have notified the Company of their intent to exercise the full over-allotment option. The offering, including the over-allotment option exercise, is expected to close on September 16, 2009, subject to customary closing conditions.

The above description of the Underwriting Agreement is qualified in its entirety by reference to the Underwriting Agreement, which is filed as Exhibit 1.1 hereto and incorporated herein by reference.

Ropes & Gray, LLP, counsel to the Company, has issued an opinion to the Company, dated September 11, 2009 regarding the legality of the issuance and sale of its common stock in the offering. A copy of the opinion as to legality is filed as Exhibit 5.1 hereto.

(d) Exhibits

      1.1        Underwriting Agreement, by and among Entegris, Inc. and Citigroup
                 Global Markets Inc., Goldman, Sachs & Co., Craig Hallum Capital
                 Group LLC, ABN AMRO Incorporated and PNC Capital Markets LLC, dated
                 September 10, 2009

      5.1        Opinion of Ropes & Gray LLP

     23.1        Consent of Ropes & Gray LLP (included in Exhibit 5.1 above).