Exhibit 21 SUBSIDIARIES OF RICHARDSON ELECTRONICS, LTD. Richardson Electronics Canada, Ltd. Canada Richardson Electronics (Europe) Ltd. United Kingdom RESA, SNC France Richardson France SNC France Richardson Electronics Italy SRL Italy Richardson Electronics Iberica, S.A. Spain Richardson Electronics GmbH Germany Richardson Electronics Japan K.K. Japan Richardson Electronics Pte Ltd. Singapore Richardson Electronics S.A. de C.V. Mexico Richardson Electronics Benelux B.V. The Netherlands Richardson Electronics do Brasil Ltda. Brasil Richardson Electronics Pty Limited Australia Tubemaster, Inc. United States