AlGaN/GaN high electron mobility transistors (HEMTs) irradiated with 1.8-MeV protons show more relative degradation in RF power/current gain, cutoff frequency , and maximum oscillation frequency than DC transconductance. These result from radiation-induced increases in fast bulk and surface trap densities, as well as increasing impedance mismatch at high frequencies with increasing proton fluence.-rich MBE devices show less degradation in DC transconductance, but more degradation in RF gain than Ga-rich devices.