Novel InP-based heterojunction bipolar transistors (HBTs) using an AlW pseudomorphic emitter, together with an InP base and collector, have been fabricated. By using InP as both base and collector, the advantages of high electron velocity and high breakdown field of InP collectors are obtained without the problem associated with the energy barrier between the more standard InGaAsAnP base and collector heterojunction. Epitaxial layers were grown by gas-source molecular beam epitaxy (GSMBE). The 200Å pseudomorphic emitter had an aluminium fraction of 15%, sufficiently suppressing hole injection from the base. The DC gain for 40×40 μm2 devices reached 18. The epibreakdown voltage BVCEO of 10V is an improvement over devices with InGaAs base and collector layers.