**Exhibit 31.1**

**CERTIFICATION**

 

I, Robert P. Akins, certify that:

 

1.               I have reviewedthis annual report on Form 10-K of Cymer, Inc.;

 

2.               Based on myknowledge, this report does not contain any untrue statement of a material factor omit to state a material fact necessary to make the statements made, inlight of the circumstances under which such statements were made, notmisleading with respect to the period covered by this report;

 

3.               Based on myknowledge, the financial statements, and other financial information includedin this report, fairly present in all material respects the financialcondition, results of operations and cash flows of the registrant as of, andfor, the periods presented in this report;

 

4.               The registrant’sother certifying officer and I are responsible for establishing and maintainingdisclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e)and 15d-15(e)) and internal control over financial reporting (as defined inExchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

 
| (a)    |   | designed such disclosure controls and procedures, or  caused such disclosure controls and procedures to be designed under our  supervision, to ensure that material information relating to the registrant,  including its consolidated subsidiaries, is made known to us by others within  those entities, particularly during the period in which this report is being  prepared; |
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| (b)    |   | designed such internal control over financial  reporting, or caused such internal control over financial reporting to be  designed under our supervision, to provide reasonable assurance regarding the  reliability of financial reporting and the preparation of financial  statements for external purposes in accordance with generally accepted  accounting principles;        |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                |
| (c)    |   | evaluated the effectiveness of the registrant’s  disclosure controls and procedures and presented in this report our  conclusions about the effectiveness of the disclosure controls and  procedures, as of the end of the period covered by this report based on such  evaluation; and                                                                                        |
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| (d)    |   | disclosed in this report any change in the  registrant’s internal control over financial reporting that occurred during  the registrant’s most recent fiscal quarter that has materially affected, or  is reasonably likely to materially affect, the registrant’s internal control  over financial reporting; and                                                   |

 

5.               The registrant’sother certifying officer and I have disclosed, based on our most recentevaluation of internal control over financial reporting, to the registrant’s auditorsand the audit committee of the registrant’s board of directors (or personsperforming the equivalent functions):

 
| (a)    |   | all significant deficiencies and material weaknesses  in the design or operation of internal control over financial reporting which  are reasonably likely to adversely affect the registrant’s ability to record,  process, summarize and report financial information; and |
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|   |   |                                                                                                                                                                                                                                                                              |
| (b)    |   | any fraud, whether or not material, that involves  management or other employees who have a significant role in the registrant’s  internal control over financial reporting.                                                                                                 |

 

 
| Date: March 16, 2005 |   |                               |
|----------------------|--------|------------------------------------|
|                 |   |                               |
|                 |   | /s/  ROBERT P. AKINS               |
|                 |   | Robert  P. Akins                   |
|                 |   | Chairman,  Chief Executive Officer |
|                 |   |                               |

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