A process of forming a three region dielectric film on silicon and a semiconductor device employing such a film are disclosed. Silicon is oxidized in an oxygen-containing ambient. The oxidation step forms a first region of silicon oxide. Once oxidation has begun, reactive sputtering of aluminum in an oxygen plasma is initiated. This forms a second region of said dielectric film which comprises a mixture of silicon and aluminum oxides. A third region comprising substantially aluminum oxide is formed by the continuing reactive sputtering step.A semiconductor device comprising said three region dielectric film interposed between an electrode and a semiconductor body has little or no shift in threshold voltage providing good stability and can be fabricated in substantially less time and/or at lower temperatures than prior art methods.