Thermal neutron irradiation produces spatially and energetically homogeneous distributed defects in n-GaAs. These defects act as majority charge carrier traps and scattering centres and as recombination sites for photogenerated charge carriers. This leads to a lowering of the charge carrier concentration and mobility and to a decrease in the maximum photocurrent. Additionally, the photocurrent onset potential is further shifted in the positive direction versus the flat band potential. Annealing of irradiated samples at temperatures below 600 degrees C leads to defect annihilation and thus to restoration of the original electrochemical properties. Annealing at temperatures above 600 degrees C results in an arsenic deficient surface with electronic defect states in the band gap in the near-surface region. Recombination at these defects appears to affect only the maximum photocurrent and not the photocurrent onset potential.