The spectral dependence of the photocurrent in Pb-Pb oxide-Pb structures is investigated varying both the electrode thickness and the resistance of the junctions. The samples exhibit sign reversal of the photocurrent with changing photon energy hν. The effect is strongly controlled by the electrode thickness and direction of illumination. Zero-bias barrier heights betwen 0.8 and 1 eV have been deduced from the threshold of the photoresponse. Onset of band-to-band excitation in the oxide film has probably been observed at hν≃2.7 eV for thermally oxidized samples and at hν≃2.9 eV for plasma-oxidized samples.