This paper reports the results of photocapacitance measurements applied to the metal SiO2-Si structure. Photocapacitance measurements under a constant capacitance condition determine the spatial distribution of deep levels existing at Si/SiO2 interface regions. The photocapacitance method revealed deep levels distributed-in a spectral region of 0.4-1.05 eV optically, and an optical level located 1.05 eV below the conduction band in the n-Si/SiO2 interface region. With respect to p-Si/SiO2, deep levels distributed at 0.4-0.85 eV and 0.85 eV, 1.05 eV levels above the valence band, were observed. Differences of interface level densities are shown as a function of Si conduction type and different preparations of oxide layers. Comparisons with the results of capacitance-voltage measurements are also discussed.