A semiconductor device and a method of making the same is disclosed. The device includes a substrate having an AlGaN layer located on a GaN layer for forming a two dimensional electron gas at an interface between the AlGaN layer and the GaN layer. The device also includes a plurality of contacts. At least one of the contacts includes an ohmic contact portion located on a major surface of the substrate. The ohmic contact portion comprises a first electrically conductive material. The at least one of the contacts also includes a trench extending down into the substrate from the major surface. The trench passes through the AlGaN layer and into the GaN layer. The trench is at least partially filled with a second electrically conductive material. The second electrically conductive material is a different electrically conductive material to the first electrically conductive material.