Abstract: A plasma and heating treatment is carried out to reduce the density of charge carrier traps adjacent the interface of an insulating layer of a thermally grown silicon dioxide and a semiconductor body. During this plasma and heating treatment, the device is covered with an additional layer of silicon containing hydrogen, such as silane, for example, and this additional layer protects the insulating layer from direct bombardment of the plasma. During and/or after the plasma treatment, heating of the structure is at about 400.degree. C. or less. After the plasma and heating treatment, the additional layer is removed from at least most parts of the semiconductor device structure.