Gallium nitride high electron mobility transistor structures enable high breakdown voltages and are usable for high-power, and/or high-frequency switching. Schottky diodes facilitate high voltage applications and offer fast switching. A superjunction formed by p/n junctions in gallium nitride facilitates operation of the high electron mobility transistor structures and Schottky diodes as well as gated diodes formed by drain to gate connections of the transistor structures. Breakdown between the gate and drain of the high electron mobility transistor structures, through the substrate, or both is suppressed.