In high-energy physics experiments, fusion experiments and other similar research, semiconductor devices may be exposed in fast neutron. This paper presents the performance and failure analysis of power devices under neutron radiation. Two thyristors with same parameters are selected to be exposed in 14.9 MeV neutron for 28 hours. It has been found that the gate trigger current, forward voltage drop, holding current and leakage current of thyristors are increased substantially after irradiation. These changes may lead to failure event. According to neutron irradiated damage theory, the failure has been studied based on the decrease of the minority carrier lifetime and the increase of the defects.