In this paper, the characteristics and device mechanism of InP/InGaAs pnp delta-doped heterojunction bipolar transistor are demonstrated. The additions of a delta-doped sheet and two spacer layers efficiently eliminate the potential spike at emitter-base junction, lower the emitter-collector offset voltage, and increase the confinement effect for electrons, simultaneously. The components of base current and the influence of delta-doped sheet on the potential spike are depicted. Experimentally, excellent device performances including a maximum current gain of 50 and a low offset voltage of 70 mV are achieved for the device with a delta-doped density of 2 x 10(12) cm(-2). The experimental results are consistent with the theoretical analysis. (c) 2006 Elsevier Ltd. All rights reserved.