Anodic oxides grown on n-InP under applied potential and illumination exhibit important blocking properties against hole transfer from the valence band. In this work we focus our attention on the blocking properties of these anodic oxides against electron transfer from the conduction band. Therefore, electron transfer which occurs during the characteristic cathodic reaction, i.e., hydrogen formation associated with semiconductor decomposition, has been studied for photo-oxidized surfaces. The cathodic behavior of n-InP previously photo-oxidized is compared to the behavior of a nonoxidized semiconductor surface. Our purpose is to study both the anodic oxide blocking properties and how the cathodic decomposition of anodic oxide-covered surfaces is modified. This work points out a complex cathodic behavior for electrodes covered with oxides. Two stages are distinguished. During the first stage of cathodic process, anodic oxide decomposition is the only reaction which takes place at the semiconductor interface. This reaction occurs with an overpotential evidencing the presence of an energetic barrier in anodic oxide. Then, when the anodic oxide is completely decomposed, a second stage occurs corresponding both to the cathodic decomposition of the semiconductor and to H-2 evolution. (C) 2004 The Electrochemical Society.