The thermal oxidation processes on cleaved surfaces of GaSe and InSe single crystals in the temperature ranges of 450-700 degrees C and 300-600 degrees C, respectively have been investigated. The photoelectric properties of the obtained heterostructures were studied. It was established that the photoconductivity peculiarities can be explained taking into consideration the nature of surface layers formed under definite conditions such as Ga2O3 (for GaSe) and In-2(SeO4)(3) or In2O3 (for InSe) oxide phases for GaSe and InSe correspondingly. It is shown that heterostructure spectral photosensitivity can be varied in a wide range due to definite selection of treatment conditions of gallium and indium monoselenides crystals e.g. temperature and duration of oxidation in air atmosphere.