In one embodiment, Group III-nitride materials are used to form a semiconductor device. A fin structure is formed in the Group III-nitride material, and a gate structure, source electrodes and drain electrodes are formed in spaced relationship to the fin structure. The fin structure provides both polar and semi-polar 2DEG regions. In one embodiment, the gate structure is configured to control current flow in the polar 2DEG region. Shield conductor layers are included above the gate structure and in spaced relationship with drain regions of the semiconductor device.