The effect of high-energy proton irradiation on GaN-based ultraviolet avalanche photodiodes (APDs) is investigated. The dark current of the GaN APD is calcu-lated as a function of the proton energy and proton flu-ences. By considering the diffusion, generation–recombination, local hopping conductivity, band-to-band tunneling, and trap-assisted tunneling currents, we found that the dark current increases as the proton fluence increases, but decreases with increasing proton energy.