Mike Thompson, serving as the U.S. Representative for California's 4th congressional district, held several committee assignments during the 118th Congress. His assignments included:

1. House Ways and Means Committee: This is a prestigious standing committee that deals with issues related to tax policy, trade, and economic policy among others. Within this committee, Mike Thompson focused primarily on matters related to health care and tax policy.

2. Subcommittee on Health (House Ways and Means Committee): As a member of this subcommittee, Thompson engaged in legislative discussions and initiatives pertaining to public health policy, Medicare, and aspects of the Affordable Care Act.

3. Subcommittee on Tax Policy (House Ways and Means Committee): His role here involved working on legislation affecting tax codes and financial policies impacting both individuals and businesses.

These assignments reflect his areas of focus especially in matters related to fiscal policies and health care reform, consistent with his long-term legislative priorities.

For more detailed information, you may refer to Congress.gov, which provides an official database for congressional committee assignments and other legislative activities.