Tin-doped indium oxide (ITO) layers are proposed as transparent conductive contact coatings on semiconductor materials for Schottky barrier photoanodes. ITO electrodes undergo substantial changes under high positive potentials (greater than 1.5 V vs. a saturated calomel electrode) in aqueous electrolytes. Longer potentiostatic stress leads to a decrease in the oxygen evolution reaction. The rate of this decrease increases with increasing electrode potential. Fluctuations of the current density are possible. It was found by a combination of radiochemical and electrochemical methods that the oxygen evolution is accompanied by electrode corrosion. After this process the electrode probably consists of an unchanged bulk and an SnO2 coating; its quasi-metallic character has disappeared.