EXHIBIT 23.1CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRMWe consent to the incorporation by reference in the following Registration Statements:(1) Registration Statement (Form S-8 No. 33-126807) pertaining to the Novellus Systems, Inc. 2001Stock Incentive Plan and Novellus Systems, Inc. Amended and Restated 1992 Employee Stock PurchasePlan, (2) Registration Statement (Form S-8 Nos. 33-62807, 333-11825, 333-35487, 333-65567, 333-80453)pertaining to the Novellus Systems, Inc. Amended and Restated 1992 Stock Option Plan, and theNovellus Systems, Inc. Amended and Restated 1992 Employee Stock Purchase Plan, (3) Registration Statement (Form S-8 No. 333-54056) pertaining to the Gasonics InternationalCorporation 1994 Stock Option/Stock Issuance Plan, and the Gamma Precision Technology 1998 StockOption Plan, (4) Registration Statement (Form S-8 No. 333-54058) pertaining to the Novellus Systems, Inc.Amended and Restated 1992 Stock Option Plan, (5) Registration Statement (Form S-8 No. 333-70146) pertaining to the Novellus Systems, Inc. 2001Stock Incentive Plan, (6) Registration Statement (Form S-8 No. 333-54056) pertaining to the GaSonics InternationalCorporation 1994 Stock Option/Stock Issuance Plan, Gamma Precision Technology 1998 Stock OptionPlan, GaSonics International Corporation 2000 Supplemental Stock Option Plan, and the NovellusSystems, Inc. 401(k) Plan, (7) Registration Statement (Form S-8 No. 333-89742) pertaining to the Novellus Systems, Inc.Amended and Restated 1992 Stock Option Plan, Novellus Systems, Inc. Amended and Restated 1992Employee Stock Purchase Plan, Novellus Systems, Inc. 2001 Stock Incentive Plan, Novellus Systems,Inc. 2001 Non-Qualified Stock Option Plan, Novellus Systems, Inc. 401(k) Plan, GaSonicsInternational Corporation 1994 Stock Option/Stock Issuance Plan, Gamma Precision Technology 1998Stock Option Plan, and the GaSonics International Corporation 2000 Supplemental Stock Option Plan, (8) Registration Statement (Form S-8 No. 333-101730) pertaining to the SpeedFam, Inc. 1991 EmployeeIncentive Stock Option Plan, as amended, SpeedFam-IPEC, Inc. 1992 Stock Option Plan, as amended,1995 Stock Plan for Employees and Directors of SpeedFam-IPEC International, Inc., as amended, 2001Nonstatutory Stock Option Plan of SpeedFam-IPEC, Inc., and the Stand-Alone Nonstatutory StockOption Agreement of SpeedFam-IPEC, Inc., dated June14, 2001, (9) Registration Statement (Form S-8 No. 333-102784) pertaining to the Novellus Systems, Inc. 2001Non-Qualified Stock Option Plan, as amended, (10) Registration Statement (Form S-8 No. 333-121248) pertaining to the Novellus Systems, Inc.Retirement Plan, and (11) Registration Statement (Form S-8 No. 333-117169) pertaining to the New Employee Stand-AloneNon-Statutory Stock Option Agreement, New Employee Stand-Alone Restricted Stock Award and theNovellus Systems, Inc. Retirement Plan;of our reports dated March 13, 2006, with respect to the consolidated financial statements andschedule of Novellus Systems, Inc., Novellus Systems, Inc.’s management’s assessment of theeffectiveness of internal control over financial reporting and the effectiveness of internalcontrol over financial reporting of Novellus Systems, Inc., included in this Annual Report (Form10-K) for the year ended December 31, 2005.                                                                                        /s/ Ernst & Young LLP         San Jose, California