A low‐pressure gas plasma of oxygen ions has been used as the electrolyte for anodizing evaporated aluminum films on glass substrates. The oxide film grows at 22Aå/v at low voltages, while above 50v, the growth rate is somewhat less. Films have been anodized up to 90v. Capacitors formed of such plasma anodized aluminum films with aluminum counterelectrodes are almost entirely free of pinholes and other faults so that they exhibit very low and nearly nonpolar leakage currents. Capacitors anodized at 50v have shown excellent electrical and life performance when operated at 20v, even at temperatures of 150°C.