A field effect transistor (FET) including a substrate, a plurality of semiconductor epitaxial layers deposited on the substrate, and a heavily doped gate layer deposited on the semiconductor layers. The FET also includes a plurality of castellation structures formed on the heavily doped gate layer and being spaced apart from each other, where each castellation structure includes at least one channel layer. A gate metal is deposited on the castellation structures and between the castellation structures to be in direct electrical contact with the heavily doped gate layer. A voltage potential applied to the gate metal structure modulates the at least one channel layer in each castellation structure from an upper, lower and side direction.