We report a microscopic study of the Au/5 Angstrom SiNx/GaAs Schottky barrier based on scanning near-field optical microscopy. Photocurrent yield microimages taken at different photon energies reveal non-topographic features. Taking into account their dependence on photon energy and bias, such features are consistent with lateral variations of the local density of states related to defects. The results, therefore, confirm that lateral variations must be considered when analyzing semiconductor interfaces and of the corresponding devices. (C) 1998 Elsevier Science B.V.