The photosensitive In2O3-p-InSe heterostructures in which the In2O3 frontal layer has a nanostructured surface were investigated. The photoresponse spectra of such heterostructures are found to be essentially dependent on surface topology of the oxide. The obtained results indicate that the In2O3 oxide is not only the active component of the structure but also acts as a diffraction cellular element. The oxide surface topology was investigated by means of the atomic-force microscope technique. It was established that the surface topology is caused by the technological conditions of growing In2O3 oxides. Under different conditions of oxidation the sample surfaces had contained nanoformations preferably in the form of nanoneedles. Their location has both a disordered and ordered character. The sizes, form and density of the nanoneedles are different, too. A dimensional optical effect in the oxide was found to be due to the anisotropic light absorption in InSe. The higher deviation of incident light from its normal direction due to a nanostructured surface is the higher variation in the generation of carriers in the semiconductor is. These changes consist in the energy broadening of the heterostructure photoresponse spectrum as well in peculiarities of the excitonic line. The higher density and ordering of the nanoneedles on the oxide surface is the higher long-wave shift and more intensive excitonic peak in spectrum takes place.