A HEMT device has a substrate; a buffer layer disposed above the substrate; a carrier supplying layer disposed above the buffer layer; a gate element penetrating the carrier supplying layer; and a drain element disposed on the carrier supplying layer. The carrier supplying layer has a non-uniform thickness between the gate element and the drain element, the carrier supplying layer having a relatively greater thickness adjacent the drain element and a relatively thinner thickness adjacent the gate element. A non-uniform two-dimensional electron gas conduction channel is formed in the carrier supplying layer, the two-dimensional electron gas conduction channel having a non-uniform profile between the gate and drain elements.