The temperature-dependent electron impact ionizations of an InP/InGaAs double heterojunction bipolar transistor (DHBT) with a step-graded InAlGaAs/InP collector structure are studied and demonstrated from 300 to 400 K. Experimentally, the multiplication factor and electron ionization coefficient are increased with increasing temperature. Furthermore, the studied device shows a lower multiplication factor and weaker temperature dependence as compared with conventional InP/InGaAs HBTs. Therefore, the studied DHBT device with a step-graded InAlGaAs/InP collector structure provides promise for low-voltage and low-power circuit applications. (c) 2007 The Electrochemical Society.