Large-area (75 mum emitter diameter) InGaP/GaAs heterojunction bipolar transistors (HBTs) were irradiated either with 40 MeV protons at fluences up to 5 x 10(9) cm(-2) or with Co-60 gamma-rays to maximum doses of 500 Mrad. Both types of radiation produced increases in generation-recombination leakage current in the emitter-base junction. The dc current gain of the HBTs decreased monotonically with increasing gamma-ray dose, but was found to increase slightly for proton irradiation due to differential changes in the base and collector resistances. The HBTs appear to be well-suited to space or nuclear industry applications.