Heterojunction diodes of indium tin oxide films sputtered ontop‐silicon using ion beam techniques display significant photovoltaic effects when exposed to sunlight. Galvanomagnetic and optical measurments confirm that the oxide films are highly degenerate transparent semiconductors. At a tin oxide concentration of 10%, we observed an open‐circuit voltage of 0.51 V, short‐circuit current of 32 mA/cm2, fill factor of 0.70, and conversion efficiency of 12%. As the concentration was raised to 70%, the voltage remained steady, the current fell to 27 mA/cm2, and the fill factor fell to 0.60.