A shielded gate field effect transistor includes a trench extending into a semiconductor region. A shield electrode is in a lower portion of the trench, and is insulated from the semiconductor region by a shield dielectric. The shield dielectric comprises first and second dielectric layers, the first dielectric layer extending between the second dielectric layer and the semiconductor region. The second dielectric layer comprises a material which during oxidation process inhibits growth of oxide along surfaces of the semiconductor region covered by the second dielectric layer. An inter-electrode dielectric overlies the shield electrode, and a gate dielectric lines upper trench sidewalls. A gate electrode is in an upper portion of the trench over the inter-electrode dielectric.