In this paper, the effects of thermal annealing on the radiated InP-based high electron mobility transistors (HEMTs) is investigated. Proton irradiation is performed with energy of 2 MeV and fluence of 5 × 1013 cm−2, and subsequently the thermal annealing experiments are carried out at 100 ℃ and 200 ℃. Both drain-source saturation current (Id,sat) and maximum transconductance (gm,max) of the radiated devices demonstrate a certain degree of recovery after annealing at 100 ℃ and 200 ℃. Id,sat and gm,max recover by the maximum values of 17.37 % and 13.66% for 10 min annealing at 100 ℃, and 12.65% and 14.54% for 5 min thermal annealing at 200 ℃. The main reason for the recovery about the DC characteristics are the restore of carrier concentration and mobility. Thermal annealing has enhanced the atoms vibration, which decreases the concentration of defects by recombination and weakens the lattice scattering by rearranging the lattice. In addition, this paper reveals that different annealing temperature and duration will have different effects on irradiated InP-based HEMTs.