An improved VBIC model for InP/InGaAs double heterojunction bipolar transistors (DHBTs) is proposed. The model accounts for the double heterojunction effect and current blocking effect with novel current expressions. New empirical formulas for the collector-base capacitance and transit time are developed to explain the mobile-charge modulation effect and the role of negative differential mobility. DC and S-parameter measurements are conducted in order to realize the whole extraction flow. The accuracy and validity of this new model and extraction strategy are demonstrated by comparisons of simulation to measurement data on DC, AC small-signal and large-signal characteristics over a wide bias region. (C) 2013 Elsevier Ltd. All rights reserved.