Forperforming radiochemical photocorrosion measurements, n-GaAs samples were irradiated with thermal neutrons. The resulting changes in charge carrier concentration and mobility are determined by far IR reflectance measurements. A great part of the neutron irradiation induced defects could be annihilated by annealing at temperatures of up to 650°C. The neutron irradiation induced defects are responsible for essential changes in photoelectrochemical characteristics of n-GaAs electrodes in aqueous electrolytes. The photocurrent onset potential is shifted in positive direction and the maximum photocurrent is decreased. After annealing treatment the original photoelectrochemical behavior is restored.