UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

(Mark One)

þ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
EXCHANGE ACT OF 1934

For the quarterly period ended December 26, 2004 or

o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
EXCHANGE ACT OF 1934

For the transition period from ________to _________

Commission file number 0-12933

LAM RESEARCH CORPORATION

4650 Cushing Parkway
Fremont, California 94538

(510) 572-0200

     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 þ NO o

     Indicate by check mark whether the registrant is an accelerated filer (as defined in Rule 12b-2 of the Exchange Act). YES þ NO o

     As of January 27, 2005, there were 139,658,906 shares of Registrant’s Common Stock outstanding.

LAM RESEARCH CORPORATION
TABLE OF CONTENTS

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PART I. FINANCIAL INFORMATION

ITEM 1. FINANCIAL STATEMENTS

LAM RESEARCH CORPORATION

(1) Derived from June 27, 2004 audited financial statements.

See Notes to Condensed Consolidated Financial Statements

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LAM RESEARCH CORPORATION

See Notes to Condensed Consolidated Financial Statements

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LAM RESEARCH CORPORATION

See Notes to Condensed Consolidated Financial Statements

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LAM RESEARCH CORPORATION

NOTE 1 — BASIS OF PRESENTATION

     The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles for interim financial information and with the instructions to Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation have been included. The accompanying unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements of Lam Research Corporation (the Company or Lam) for the fiscal year ended June 27, 2004, which are included in the Annual Report on Form 10-K, File Number 0-12933. The Company’s Form 10-K, Forms 10-Q and Forms 8-K are available online at the Securities and Exchange Commission website on the Internet. The address of that site is http://www.sec.gov. The Company also posts the Form 10-K, Forms 10-Q and Forms 8-K on the corporate website at http://www.lamrc.com.

     The Company’s reporting period is a 52/53-week fiscal year. The Company’s current fiscal year will end June 26, 2005 and includes 52 weeks. The quarter ended December 26, 2004 and the quarter ended December 28, 2003 both included 13 weeks.

     Reclassifications: Certain amounts presented in the comparative financial statements for prior years have been reclassified to conform to the fiscal 2005 presentation.

NOTE 2 — RECENT ACCOUNTING PRONOUNCEMENTS

     In March 2004, the Emerging Issues Task Force (EITF) reached a consensus on recognition and measurement guidance previously discussed under EITF 03-01. The consensus clarifies the meaning of other-than-temporary impairment and its application to investments classified as either available-for-sale or held-to-maturity under Statement of Financial Accounting Standards (SFAS) 115, “Accounting for Certain Investments in Debt and Equity Securities,” and investments accounted for under the cost method or the equity method. In September 2004, the Financial Accounting Standards Board (FASB) issued a final FASB Staff Position, (FSP) EITF Issue 03-01-1, which indefinitely delays the effective date for the measurement and recognition guidance of EITF 03-01. The Company is currently evaluating the impact, if any, of adopting EITF 03-01.

     In November 2004, the FASB issued SFAS No. 151, “Inventory Costs — An Amendment of ARB No. 43, Chapter 4,” which clarifies the accounting for abnormal amounts of idle facility expense, freight, handling costs and wasted material (spoilage). The Company is required to adopt SFAS No. 151 in fiscal year 2006 and its adoption is not expected to have a significant impact on the Company’s results of operations or financial position.

     In December 2004, the FASB issued SFAS No. 123 (revised 2004), “Share-Based Payment.” This Statement is a revision of SFAS No. 123, “Accounting for Stock-Based Compensation”, and supersedes Accounting Principles Board (APB) Opinion No. 25, “Accounting for Stock Issued to Employees”, and its related implementation guidance. SFAS No. 123(R) requires that compensation cost relating to share-based payment transactions be recognized in the financial statements. That cost will be measured based on the fair value of the equity or liability instruments issued. This statement is effective beginning with the first interim or annual period after June 15, 2005, with early adoption permitted. The Company has no plans for early adoption.

     The effects of the adoption of SFAS No. 123(R) on the Company’s results of operations and financial position are dependent upon a number of factors, including the number of employee stock options outstanding and unvested, the number of employee stock options which may be granted in the future, the future market value and volatility of the Company’s stock price, movements in the risk free rate of interest, stock option exercise and forfeiture patterns, and the stock option valuation model used to estimate the fair value of each option. As a result of these variables it is not yet possible to reliably estimate the effect of the adoption of SFAS No. 123(R) on the Company’s results of operations and financial position. Note 3 herein provides an indication of the effects of adoption assuming the use of the Black Scholes option pricing model and the assumptions detailed therein to estimate the fair value of employee stock options and employee stock purchase plan awards upon the results of operations for the three and six months ended December 26, 2004 and December 28, 2003.

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     In December 2004, the FASB issued SFAS No. 153, “Exchanges of Nonmonetary Assets, an amendment of APB Opinion No. 29.” The amendments made by SFAS No. 153 are based on the principle that exchanges of nonmonetary assets should be measured based on the fair value of the assets exchanged. SFAS No. 153 also eliminates the exception for nonmonetary exchanges of similar productive assets and replaces it with a broader exception for exchanges of nonmonetary assets that do not have commercial substance. SFAS No. 153 is effective for nonmonetary asset exchanges occurring in fiscal periods beginning after June 15, 2005. The Company will apply its provisions prospectively upon adoption and its adoption is not expected to have a significant impact on the Company’s results of operations or financial position.

NOTE 3 — STOCK-BASED COMPENSATION PLANS

     The Company has adopted stock option plans that provide for the grant to employees of various equity incentive awards, including options to purchase shares of Lam common stock. In addition, the plans permit the grant of nonstatutory stock options to paid consultants and provide for the automatic grant of nonstatutory stock options to outside directors. The Company also has an employee stock purchase plan (ESPP) that allows employees to purchase its common stock.

     The Company accounts for its stock option plans and stock purchase plan under the provisions of APB Opinion No. 25, “Accounting for Stock Issued to Employees” (APB 25) and FASB Interpretation (FIN) 44, “Accounting for Certain Transactions Involving Stock Compensation — an Interpretation of APB Opinion No. 25” (FIN 44). Pro forma information regarding net income (loss) and net income (loss) per share is required by SFAS No. 123, “Accounting for Stock-Based Compensation”, as amended by SFAS No. 148, “Accounting for Stock-Based Compensation-Transition and Disclosure” as if the Company had accounted for its stock option and stock purchase plans under the fair value method of SFAS No. 123 and SFAS No. 148. The following table illustrates the effect on net income and net income per share if the Company had accounted for its stock option and stock purchase plans under the fair value method of accounting under SFAS No. 123 and SFAS No. 148:

     For pro forma purposes, the estimated fair value of the Company’s stock-based awards is amortized over the options’ vesting period (for options) and the respective four, eight, twelve, or sixteen-month purchase periods (for stock purchases under the employee stock purchase plan). The fair value of the Company’s stock options and stock purchase plan awards were estimated using a Black-Scholes option valuation model, which was developed for use in estimating the fair value of traded options which have no vesting restrictions and which are fully transferable. The model requires the input of highly subjective assumptions, including expected stock price volatility and the estimated life of each option. The fair value of all of the Company’s stock-based awards was estimated assuming no expected dividends and estimates of expected life, volatility and risk-free interest rate at the time of grant. The fair value of the Company’s stock-based awards granted in the three and six-month periods of fiscal 2005 and fiscal 2004 was estimated using the following weighted-average assumptions:

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NOTE 4 — INVENTORIES

     Inventories are stated at the lower of cost (first-in, first-out method) or market. Inventories consist of the following:

NOTE 5 — PROPERTY AND EQUIPMENT

     Property and equipment, net, consist of the following:

NOTE 6 — ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES

     Accrued expenses and other current liabilities consist of the following:

NOTE 7 — OTHER INCOME, NET

     The significant components of other income, net, are as follow:

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NOTE 8 — NET INCOME PER SHARE

     Basic net income per share is computed by dividing net income by the weighted-average number of common shares outstanding during the period. Diluted net income per share is computed, using the treasury stock method, as though all potential common shares that are dilutive were outstanding during the period. The following table provides a reconciliation of the numerators and denominators of the basic and diluted computations for net income per share.

     For purposes of computing diluted net income per share, weighted-average common shares do not include potential dilutive securities whose exercise prices exceed the average market value of the Company’s common stock for the period. The following potential dilutive securities were excluded:

     In addition, during the three and six months ended December 28, 2003, 6.7 million potential dilutive securities related to the Company’s convertible subordinated 4% notes (4% Notes) were excluded for purposes of computing diluted net income per share because the effect would have been antidilutive. The Company’s 4% Notes were repaid in June, 2004, two years prior to maturity.

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NOTE 9 — COMPREHENSIVE INCOME

     The components of comprehensive income are as follows: