Exhibit 10.1

Cymer Inc.

2H 2009 Bonus Plan

Summary Description

On August 19, 2009, the Compensation Committee (the “Compensation Committee”) of
Cymer’s Board of Directors approved a financial performance-based cash bonus
program for the second half of fiscal 2009 (the “2H-2009 Plan”).

Eligibility: All employees eligible to participate under either Cymer’s Profit
Sharing Plan or its Short-Term Incentive Plan are eligible to participate in the
2H-2009 Plan. Cymer employees may not participate in both the Profit Sharing
Plan and the Short-Term Incentive Plan. The participant must be employed by
Cymer at the time of payment in order to receive payment under the 2H-2009 Plan.

Plan Calculation: The total amount available to be paid to eligible employees as
cash bonuses under the 2H-2009 Plan (“Total Available Bonus Amount”) will be
equal to the amount by which Cymer’s operating income for the third and fourth
quarters of fiscal 2009, combined, exceeds a specified base amount established
by the Committee, multiplied by 40%. However, eligible Cymer employees will be
paid a cash bonus only if Cymer recognizes operating income during the third and
fourth quarters of fiscal 2009, combined, in excess of a separate specified
threshold level established by the Committee.

Each eligible employee’s individual bonus amount paid under the 2H-2009 Plan
will be equal to the Total Available Bonus Amount multiplied by a fraction, the
numerator which will be such employee’s target bonus award under the Profit
Sharing Plan or the Short-Term Incentive Plan, as applicable, and the
denominator of which will be the aggregate amount of all eligible employees’
target bonus awards under the Profit Sharing Plan and the Short-Term Incentive
Plan.

Annual Maximum. The maximum aggregate amount that may accrue under the 2H-2009
Plan and Cymer’s Long-Term Incentive Program together in 2009 is 15% of Cymer’s
adjusted EBITDA (earnings before interest, taxes, depreciation, amortization and
compensation expense attributable to stock awards). If the aggregate bonus
amount accrued under both plans would exceed this cap, bonus awards would be
adjusted downward to a total of 15% of Cymer’s adjusted EBITDA for fiscal 2009.

Disclaimer: Cymer reserves the right to modify the 2H-2009 Plan at any time.