According to one embodiment of the present disclosure, the body portion 122 of the first electrode 120 may be in direct contact with and electrically connected to the semiconductor barrier layer 106. The bottom surface 122B of the body portion 122 may be level with or deeper than the top surface 106T of the semiconductor channel layer 106. The vertical extension portion 126 of the first electrode 120 may extend downward from the bottom surface 122B of the body portion 122, so that the bottom surface 126B of the vertical extension portion 126 may be lower than the top surface 104T of the semiconductor buffer layer 104. The vertical length Lv of the vertical extension portion 126 may be 0.5 μm to 3 μm, but not limited thereto. In addition, since the dielectric layer 116 is disposed between the vertical extension portion 126 and the underlying layers (i.e., the semiconductor channel layer 106 and the semiconductor buffer layer 104), it is possible to prevent current from flowing from the vertical extension portion 126 into the semiconductor channel layer 106 or the semiconductor buffer layer 104. The horizontal extension portion 124 of the first electrode 120 may extend from one side of the body portion 122 toward the gate electrode 112. The horizontal length Lh of the horizontal extension portion 124 may be 0.5 μm to 3 μm, but not limited thereto. In addition, since the dielectric layer 116 is disposed between the horizontal extension portion 124 and the semiconductor barrier layer 108, it is possible to prevent current from flowing from the horizontal extension portion 124 into the semiconductor barrier layer 108. The first electrode 120, the second electrode 130, and the gate electrode 112 may be single-layer or multi-layer structures, and their compositions can include low-resistance semiconductors, metals, or alloys, such as Al, Cu, W, Au, Pt, Ti, and polysilicon, but not limited thereto. In addition, the first electrode 120 and the second electrode 130 may form ohmic contact with the underlying semiconductor channel layer 106.