Abstract: A semiconductor substrate includes: a base substrate layer doped with a first type dopant; a first epitaxial layer on the base substrate layer that has a first thickness and is doped with the first type dopant to provide a first resistivity; a second epitaxial layer on the first epitaxial layer that has a second thickness and is doped with the first type dopant to provide a second resistivity (less than the third resistivity); and a third epitaxial layer on the second epitaxial layer that has a third thickness and is doped with the first type dopant to provide a third resistivity (less than the second resistivity). An oxide field trench transistor includes a trench with insulated polygate and polysource regions extending into the semiconductor substrate and passing through the first doped region, the second doped region, the third epitaxial layer and partially into the second epitaxial layer.