Among possible losses in the efficiency of semiconductor photodiodes and solar cells, optical losses are dominant in many cases and, therefore, are important. The optical losses, mainly consisting of reflection from the surface and absorption in a dead layer, are evaluated based on a theoretical model whose validity was confirmed by experiments. The effect of the surface layer on the optical properties of the whole system is analysed, using a complex plane representation of reflectance and transmittance, to be quite important, and is sensitive to its layer thickness and the angle of incidence. The results are presented as a function of wavelength, surface film thickness and angle of incidence. The results show that the optical properties of the layered system are completely different from those of a single boundary system and change steeply in the UV range due to the change in optical indices of both the surface layer and the substrate.