The flat band potential and the possible use of a Schottky barrier model for the description of the electrolyte/ZnSe interface indicate that in a large potential domain (vs. e.s.m.), ranging between −1.0 and +10.0 V, the semiconductor space charge region is a depletion layer. This fact enables the use of the electrolyte electroreflectance technique in the case of a fully depleted layer as an in situ method of study of the electrochemical behavior of zinc selenide. Over the electrode potential ranges between −1.0 and +6.0 V, the ZnSe decomposition gives soluble products and for potentials higher than +6.0 V the final result of the decomposition is the formation of a zinc oxide layer. The shape and energetic position of the electroreflectance spectra show that in the first case the ZnSe electrode surface remains unchanged whereas in the second case a surface transformation appears which is irreversible. These results correlate with data obtained in a purely electrochemical way.