InP-based high electron mobility transistors (HEMTs) will be affected by protons from different directions in space radiation applications.The proton irradiation effects on InAlAs/InGaAs hetero-junction structures of InP-based HEMTs are studied at incident angles ranging from 0 to 89.9° by SRIM software.With the increase of proton incident angle,the change trend of induced vacancy defects in the InAlAs/InGaAs hetero-junction region is consistent with the vacancy energy loss trend of incident protons.Namely,they both have shown an initial increase,followed by a decrease after incident angle has reached 30°.Besides,the average range and ultimate stopping positions of incident protons shift gradually from buffer layer to hetero-junction region,and then go up to gate metal.Finally,the electrical characteristics of InP-based HEMTs are investigated after proton irradiation at different incident angles by Sentaurus-TCAD.The induced vacancy defects are considered self-consistently through solving Poisson’s and current continuity equations.Consequently,the extrinsic transconductance,pinch-off voltage and channel current demonstrate the most serious degradation at the incident angle of 30°,which can be accounted for the most severe carrier sheet density reduction under this condition.