A semiconductor device which includes a polysilicon gate separated from a semiconductor substrate by a re-oxidized nitrided oxide film in which the concentration of re-oxidized nitride in the film underlying the gate is non-uniform and in which the concentration of nitrogen in the substrate and the re-oxidized nitrided oxide along their interface and underlying the gate is non-uniform. Methods are disclosed of providing the non-uniform concentrations by incomplete shielding of the oxide by the gate during the nitriding and re-oxidizing process.