An experimental and theoretical study of GaAs and GaP Schottky photodiode quantum efficiency is reported. The quantum efficiency was investigated as a function of temperature in the 80-360 K interval and as a function of electric field in the space-charge region in the interval. The photocurrent is found to increase strongly with temperature, by a factor of three for GaP diodes and by a factor of six for GaAs diodes. We believe that this is evidence of a high concentration of imperfections in the space-charge region. These imperfections manifest themselves only in photoelectric properties. Such defects act as traps and capture both photoelectrons and photoholes. At low temperatures, most of the pairs recombine, but some fraction of them escape from the traps due to thermal excitation and give an electric current which rises with temperature. The time of the capture has to be of the order of the carrier drift time, . The electric field dependence of the quantum efficiency is also evidence of the high trap concentration. We believe that this is due to a field-induced shift of the carrier energy level in the trap. At high temperature, the photon energy and electric field dependencies of the photocurrent tend towards saturation.