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Neutron, proton, and electron irradiation effects in InGaP/GaAs single heterojunction bipolar transistors are investigated. Devices with different emitter sizes and grown by two different growth techniques are studied. At low fluences of proton and neutron irradiation, a small gain increase is observed at low base currents. At higher fluences, gain degradation is observed whose magnitude depends on the nature and fluence of the irradiation particle. In the case of electron irradiation, the change in gain is very small for electron fluence up to 7×1015 e/cm2 although a careful analysis shows a slight gain increase at low base currents and a slight gain degradation at higher base currents. The gain increase at small base currents and low fluence is believed to be caused by the ionization damage in the polyimide passivation layer. The gain degradation at higher fluence and high base currents is due to the displacement damage in the emitter-base junction region. In addition to the gain degradation, neutron irradiation causes a shift of the emitter-base offset voltage, which is caused by the displacement damage in the base-collector region. The correlation of the gain degradation coefficients for the different particles is discussed in the framework of the NIEL theory.