A dimpled substrate and method of making including a substrate of high thermal conductivity having a first main surface and a second main surface opposite the first main surface. Active epitaxial layers are formed on the first main surface of the substrate. Dimples are formed as extending from the second main surface into the substrate toward the first main surface. An electrical contact of low resistance material is disposed on the second main surface and within the dimples. A back contact of low resistance and low loss is thus provided while maintaining the substrate as an effective heat sink.