Bipolar power transistors (BPTs) are widely used in various kinds of high-voltage and medium-power applications due to their low on-state voltage drop and high current capability. In this paper, the influence of minority carrier extracted by the base electrode on the current gain of BPTs is presented first and studied in detail. It is suggested that the minority carrier extracted by the base electrode is responsible for the current gain change. Based upon this theory, a structure with a local heavily-doped base (LHDB) to increase the current gain is proposed and investigated. The increase of the current gain can be controlled by the doping of the LHDB and the location of the LHDB relative to the emitter region. The analytical results show a good agreement with the numerical simulation and experiment results. (c) 2006 Elsevier Ltd. All rights reserved.