AlGaAs/GaAs single heterojunction bipolar transistors grown on InP substrates by molecular beam epitaxy have been fabricated and tested. An eight‐period 25 Å/25 Å In0.53Ga0.47As/GaAs strained‐layer superlattice is incorporated in the buffer structure to reduce dislocation propagation to the active region. Small‐signal common emitter current gains of about 20 and 30 at a collector current density of 2×103 A/cm2 have been obtained for devices on InP as compared to about 60 and 150 for those on GaAs in structures with base thickness of 0.12 μm doped with Be to 1×1019 and 1×1018 cm-3, respectively. Current densities as high as 1×104 A/cm2 have been achieved in these devices with emitter area of 50×50 μm2 without degradation, demonstrating the excellent stability of this material. From the collector current dependence of the current gain, ideality factors of 1.3 and 1.2 for the emitter junctions have been obtained for devices on InP and GaAs, respectively.