We investigate the effect of thermal annealing in argon and of oxygen plasma processing on the photoelectric properties of GaAs-Ga2O3-Me structures. Gallium-oxide films are fabricated by photostimulated electrochemical oxidation of epitaxial gallium-arsenide layers with n-type conductivity. The as-deposited films were amorphous, but their processing in oxygen plasma led to the nucleation of β-Ga2O3 crystallites. The unannealed films are nontransparent in the visible and ultraviolet (UV) ranges and there is no photocurrent in structures based on them. After annealing at 900°C for 30 min, the gallium-oxide films contain only β-Ga2O3 crystallites and become transparent. Under illumination of the Ga2O3-GaAs structures with visible light, the photocurrent appears. This effect can be attributed to radiation absorption in GaAs. The photocurrent and its voltage dependence are determined by the time of exposure to the oxygen plasma. In the UV range, the sensitivity of the structures increases with decreasing radiation wavelength, starting at λ ≤ 230 nm. This is due to absorption in the Ga2O3 film. Reduction in the structure sensitivity with an increase in the time of exposure to oxygen plasma can be caused by the incorporation of defects both at the Ga2O3-GaAs interface and in the Ga2O3 film.