A semiconductor device includes a semiconductor layer with opposing first and second main surfaces and a first column extending from the first main surface and having a first concentration of a dopant of the first conductivity type. A trench with a sidewall and bottom extends at least partially through the semiconductor layer from the first main surface. A second column between the trench sidewall and the first column has a second concentration of a dopant of a second conductivity type and is formed in the semiconductor layer and extends from the first main surface. A trench oxide layer is in contact with at least the trench sidewall and the trench bottom. A trench nitride layer covers the trench oxide layer at least on the trench sidewall. A dielectric seal material seals the trench proximate the first main surface of the semiconductor layer such that the trench is air-tight.