A semiconductor power device includes a substrate of a first conductivity type and an epitaxial layer of the first conductivity type over and in contact with the substrate. A first trench extends into and terminates within the epitaxial layer. A sinker trench extends from the top surface of the epitaxial layer through the epitaxial layer and terminates within the substrate. The sinker trench is laterally spaced from the first trench, and is wider and extends deeper than the first trench. The sinker trench is lined with an insulator only along the sinker trench sidewalls so that a conductive material filling the sinker trench makes electrical contact with the substrate along the bottom of the trench and makes electrical contact with an interconnect layer along the top of the trench.