Abstract: A high breakdown voltage HFET includes a reduced surface field (RESURF) layer of p-type conductivity GaN positioned on a substrate with a channel layer of n-type conductivity GaN positioned thereon. A barrier layer of n-type conductivity Al.sub.x Ga.sub.1-x N is positioned on the channel layer to form a lateral channel adjacent to and parallel with the interface. A gate electrode is positioned on the barrier layer overlying the lateral channel and a drain electrode is positioned on the channel layer in contact with the lateral channel and spaced to one side of the gate electrode a distance which determines the breakdown voltage. A source electrode is positioned on the channel layer to the opposite side of the gate electrode, in contact with the lateral channel and also in contact with the RESURF layer.