AlGaN/GaN high electron mobility transistors(HEMTs) were exposed to 1 MeV neutron irradiation at a neutron fluence of 1 × 10 15 cm 2.The dc characteristics of the devices,such as the drain saturation current and the maximum transconductance,decreased after neutron irradiation.The gate leakage currents increased obviously after neutron irradiation.However,the rf characteristics,such as the cut-off frequency and the maximum frequency,were hardly affected by neutron irradiation.The AlGaN/GaN heterojunctions have been employed for the better understanding of the degradation mechanism.It is shown in the Hall measurements and capacitance-voltage tests that the mobility and concentration of two-dimensional electron gas(2DEG) decreased after neutron irradiation.There was no evidence of the full-width at half-maximum of X-ray diffraction(XRD) rocking curve changing after irradiation,so the dislocation was not influenced by neutron irradiation.It is concluded that the point defects induced in AlGaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradations of AlGaN/GaN HEMT devices. AlGaN / GaN high electron mobility transistors (HEMTs) were exposed to 1 MeV neutron irradiation at a neutron fluence of 1 × 10 15 cm 2. The dc characteristics of the devices, such as the drain saturation current and the maximum transconductance, decreased after neutron irradiation. gate leakage currents obviously obviously after neutron irradiation. Despite the rf characteristics, such as the cut-off frequency and the maximum frequency, were not affected by neutron irradiation. AlGaN / GaN heterojunctions have been employed for the better understanding of the degradation mechanism. It is shown in the Hall measurements and capacitance-voltage tests that the mobility and concentration of two-dimensional electron gas (2DEG) decreased after neutron irradiation. Here was no evidence of the full-width at half-maximum of X -ray diffraction (XRD) rocking curve changing after irradiation, so the dislocation was not influenced by neutron irradiation. It is concluded that the point defects induced in A lGaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradation of AlGaN / GaN HEMT devices.