Abstract: In a semiconductor device, a trench is etched into a surface of a semiconductor body comprising, from the surface down, a highly doped first (source) region; a moderately doped second (body) region; and a lightly doped third (drain) region. The trench walls are then oxidized. For reducing the effects of etching rate and oxide growing rate variations which occur at the junctions between regions of differing concentrations, the trench is first formed by etching and the trench walls then oxidized prior to the formation of the first region. Trenches having straighter walls and more uniformly thick oxides are thus formed.