A method of forming a semiconductor device includes providing an engineered substrate, forming a gallium nitride layer coupled to the engineered substrate, forming a channel region coupled to the gallium nitride layer by forming an aluminum gallium nitride barrier layer on the front surface of the gallium nitride layer, forming a gate dielectric layer coupled to the aluminum gallium nitride barrier layer in the central portion of the channel region, forming a gate contact coupled to the gate dielectric layer, forming a source contact at the first end of the channel region, forming a via at the second end of the channel region, filling the via with a conductive material, forming a drain contact coupled to the via, removing the engineered substrate to expose the back surface of the epitaxial gallium nitride layer, and forming a drain pad on the back surface of the epitaxial gallium nitride layer.