The photoelectrochemical behaviour of the oxygen evolving n-RuS2 \ H2SO4 interface was investigated with the help of the scanning microscope for semiconductor characterization. Electrolyte electroreflectance and photovoltage digital images were obtained as a function of the pretreatment of the RuS2 surface (polishing and electrochemical etching). Polishing gives rise to an inhomogeneous, scarcely photoactive surface, while electrochemical etching destroys the damaged overlayer generated by polishing, leaving an inhomogeneous, highly photoactive surface in contact with the electrolyte. In general, more photoactive zones are characterized by a higher electrolyte electroreflectance signal (EER-s) generated at the interfacial hydroxide layer, and a smaller signal coming from the space charge layer. According to the observed influence of the donor concentration on the EER-s signal amplitude, the contrast observed in the EER-s image was attributed to lateral heterogeneities in the donor concentration. The difficulty of modulating the electric field in the hydroxide layer at relatively high frequencies was attributed to the low relaxation time constant of surface states involved in the EER-s signal. The fact that at low light modulation frequencies those zones with the highest EER-s amplitude also show the highest photovoltage indicates that the photovoltage intensity depends on the time constant.