<PAGE>

                                                                    EXHIBIT 12.1
CERTIFICATION OF THE CHIEF EXECUTIVE OFFICER

I, Doug J. Dunn, certify that:

1. I have reviewed this annual report on Form 20-F of ASML Holding N.V.;

2. Based on my knowledge, this report does not contain any untrue statement of a
   material fact or omit to state a material fact necessary to make the
   statement made, in light of the circumstances under which such statements
   were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial
   information included in this report, fairly present in all material respects
   the financial condition, results of operations and cash flows of the company
   as of, and for, the periods presented in this report;

4. The company's other certifying officer(s) and I are responsible for
   establishing and maintaining disclosure controls and procedures (as defined
   in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the company 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 company, 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;

   b) Evaluated the effectiveness of the company'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

   c) Disclosed in this report any change in the company's internal control over
      financial reporting that occurred during the period covered by the annual
      report that has materially affected, or is reasonably likely to materially
      affect, the company's internal control over financial reporting; and

5. The company's other certifying officer(s) and I have disclosed, based on our
   most recent evaluation of internal control over financial reporting, to the
   company's auditors and the audit committee of the company's board of
   directors (or persons performing 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 company's ability to record,
      process, summarize and report financial information; and

   b) Any fraud, whether or not material, that involves management or other
      employees who have a significant role in the company's internal control
      over financial reporting.

Date: January 30, 2004

/s/ Doug J. Dunn
------------------------
Doug J. Dunn,
Chief Executive Officer


<PAGE>

CERTIFICATION OF THE CHIEF FINANCIAL OFFICER

I, Peter T.F.M. Wennink, certify that:

1. I have reviewed this annual report on Form 20-F of ASML Holding N.V.;

2. Based on my knowledge, this report does not contain any untrue statement of a
   material fact or omit to state a material fact necessary to make the
   statement made, in light of the circumstances under which such statements
   were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial
   information included in this report, fairly present in all material respects
   the financial condition, results of operations and cash flows of the company
   as of, and for, the periods presented in this report;

4. The company's other certifying officer(s) and I are responsible for
   establishing and maintaining disclosure controls and procedures (as defined
   in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the company 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 company, 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;

   b) Evaluated the effectiveness of the company'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

   c) Disclosed in this report any change in the company's internal control over
      financial reporting that occurred during the period covered by the annual
      report that has materially affected, or is reasonably likely to materially
      affect, the company's internal control over financial reporting; and

5. The company's other certifying officer(s) and I have disclosed, based on our
   most recent evaluation of internal control over financial reporting, to the
   company's auditors and the audit committee of the company's board of
   directors (or persons performing 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 company's ability to record,
      process, summarize and report financial information; and

   b) Any fraud, whether or not material, that involves management or other
      employees who have a significant role in the company's internal control
      over financial reporting.

Date: January 30, 2004

/s/ Peter T.F.M. Wennink
---------------------------
Peter T.F.M. Wennink
Chief Financial Officer