Luminescence degradation of hydride vapor-phase epitaxy-grown GaN wafers under electron-beam (e-beam) irradiation was studied. A drastic decrease in the band-edge emission is observed under e-beam irradiation. This degradation may be decomposed into two components: a strong and quick decrease in the first minute and a smaller and more gradual decrease. It is found that the vacuum condition also affects the luminescence of GaN since the degradation amplitude becomes smaller when the specimens are kept in ultrahigh vacuum. These results suggest that the adsorbed species at the surface may affect the luminescence properties of GaN.