A selenium rectifier hasis about the same size as a copper-oxide rectifiersrectifier, but is much larger than a silicon or germanium diode. Selenium rectifiers have a long but not indefinite service life of 60,000 to 100,000 hours, depending on rating and cooling. The rectifier can show some unforming of the rectifier characteristic after long storage.<ref>Ernst Bleule (ed.), ''Electronic methods'', Academic Press, 1964, {{ISBN|0-12-475902-5}}, pages 206–207.</ref> Each cell can withstand a reverse voltage around 25 volts and has a forward voltage drop around 1 volt, which limits the efficiency at low voltages. Selenium rectifiers have an [[operating temperature]] limit of 130 °C and are not suitable for high-frequency circuits.<ref>H. P. Westman (ed), ''Reference Data for Radio Engineers Fifth Edition'', Howard W. Sams & Co., Inc. 1968, chapter 13.</ref>
