MONOLITHIC POWER SYSTEMS INC

Evaluation of Disclosure Controls and Procedures

Our management, with the participation of our Chief Executive Officer and Chief Financial Officer, evaluated the effectiveness of our disclosure controls and procedures pursuant to Rule 13a-15(e) and Rule 15d-15(e) under the Securities Exchange Act of 1934 as of the end of the period covered by this Annual Report on Form 10-K.

Based on this evaluation, and due to the finding of the material weakness described below, our Chief Executive Officer and Chief Financial Officer concluded that, as of December 31, 2025, our disclosure controls and procedures were not effective to provide reasonable assurance that information we are required to disclose in reports that we file or submit under the Exchange Act is recorded, processed, summarized, and reported within the time periods specified in the SEC’s rules and forms.

Notwithstanding the material weakness in internal control over financial reporting and the resulting restatement described below, management believes and has concluded that the consolidated financial statements included in this Annual Report on Form 10-K fairly present, in all material respects, our financial position, results of operations and cash flows for the periods presented in conformity with GAAP.

Management’s Report on Internal Control over Financial Reporting

Our management is responsible for establishing and maintaining adequate internal control over financial reporting. Our management conducted an evaluation of the effectiveness of our internal control over financial reporting based on the framework inInternal Control—Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission. A material weakness is a deficiency, or a combination of deficiencies, in internal control over financial reporting, such that there is a reasonable possibility that a material misstatement of our annual or interim consolidated financial statements will not be prevented or detected on a timely basis.

As of December 31, 2025, we identified a material weakness in our internal control over financial reporting. During the year-end financial reporting process for fiscal year 2025, the material weakness was identified in internal control over financial reporting related to the accounting for deferred income taxes. We engaged third-party tax service providers in connection with the original determination of the accounting for deferred income taxes associated with a one-time tax incentive granted by a certain foreign jurisdiction. Nevertheless, the internal controls in place with respect to the review of the calculation of deferred income taxes and the related income tax expense (benefit) were not designed appropriately or operating effectively as of December 31, 2025 and 2024.

We have developed a remediation plan for this material weakness, which is described below.

As further described in Note 2 and Note 17 to the Consolidated Financial Statements, the identified material weakness resulted in the misstatement of deferred income taxes and income tax benefit, net for the fiscal year ended December 31, 2024. Ernst & Young LLP independently assessed the effectiveness of our internal control over financial reporting, as stated in the firm’s attestation report, which appears in Part II, Item 8 of this Annual Report on Form 10-K.

Remediation

Management has been implementing and continues to implement measures designed to ensure that control deficiencies contributing to the material weakness are remediated, such that these controls are designed, implemented, and operating effectively. These remediation actions are ongoing and include or are expected to include:

As we continue to evaluate and work to improve our internal control over financial reporting, we may decide to take additional measures to address this identified deficiency or modify the remediation plans described above. We believe that these actions will remediate the material weakness, however, the material weakness will not be considered remediated until the applicable controls operate for a sufficient period of time and management has concluded, through testing, that these controls are operating effectively.

Management believes the foregoing plans will effectively remediate the deficiency constituting the material weakness and believes that the remediation of this material weakness (including necessary testing) will be completed during 2026. However, there can be no assurance as to when such remediation will be completed. As the remediation plan is implemented, management may take additional measures or modify the remediation plan elements described above.

Changes in Internal Control over Financial Reporting

Except for the remediation measures related to the material weakness described above, there were no changes in our internal control over financial reporting that occurred during the quarter ended December 31, 2025, that would have materially affected, or were reasonably likely to materially affect, our internal control over financial reporting.

Limitations on Effectiveness of Controls and Procedures

In designing and evaluating the disclosure controls and procedures, management recognizes that any controls and procedures, no matter how well designed and operated, can provide only reasonable assurance of achieving the desired control objectives. In addition, the design of disclosure controls and procedures must reflect the fact that there are resource constraints, and that management is required to apply its judgment in evaluating the benefits of possible controls and procedures relative to their costs.