It has been established, by electrical and electron‐optical studies, that the oxide surface layer is responsible for the particularly stable properties of stainless steel when used for high‐voltage electrodes. The growth of this surface oxide has been studied ellipsometrically. After cleaning the surface by electron bombardment the growth of the layer was monitored in the pressure range 10−8Torr‐atmospheric pressure, and the temperature range 300–1300°K. The equilibrium thickness at room temperature and at atmospheric pressure is [inverted lazy s]30 Å. A temperature in excess of 1000°C is required to remove the film at 10−8Torr.