In one embodiment, a method for forming a semiconductor device includes forming trench and a dielectric layer along surfaces of the trench. A shield electrode is formed in a lower portion of the trench and the dielectric layer is removed from upper sidewall surfaces of the trench. A gate dielectric layer is formed along the upper surfaces of the trench. Oxidation-resistant spacers are formed along the gate dielectric layer. Thereafter, an interpoly dielectric layer is formed above the shield electrode using localized oxidation. The oxidation step increases the thickness of lower portions of the gate dielectric layer. The oxidation-resistant spacers are removed before forming a gate electrode adjacent the gate dielectric layer.