In one general aspect, an apparatus can include a semiconductor substrate, and a trench defined within the semiconductor substrate and having a depth aligned along a vertical axis, a length aligned along a longitudinal axis, and a width aligned along a horizontal axis. The apparatus includes a dielectric disposed within the trench, and an electrode disposed within the dielectric and insulated from the semiconductor substrate by the dielectric. The semiconductor substrate can have a portion aligned vertically and adjacent the trench, and the portion of the semiconductor substrate can have a conductivity type that is continuous along an entirety of the depth of the trench. The apparatus is biased to a normally-on state.