A new method to extract the effective channel length of a double-diffused MOSFET (DMOSFET) is proposed. This method models the DMOSFET by two MOSFETs serially connected each other, and extracts their channel lengths by fitting the effective channel length versus gate-voltage relation calculated by the present model to the measured one. The effective channel lengths extracted by this method is verified to be useful. (C) 2003 Elsevier Science Ltd. All rights reserved.