Mott‐Schottky plots for electrolyte junctions under various illuminations show that the semiconductor bandedges are shifted with respect to their position in the dark, the magnitude of the shift increasing with increasing light intensity. Correlatively, the surface‐state capacitance presents a sharp peak; its height increases with illumination. A model for the electron occupation rate of a surface‐state distribution is described in order to interpret these experimental facts. It is shown that such a kinetic model explains only impedance results; chemical modifications at the surface have to be invoked to account for the flatband‐potential shift at the illuminated electrode. The surface‐state capture cross sections are pulled from impedance analysis through the relaxation time .