A semiconductor device includes a first compound semiconductor material and a second compound semiconductor material on the first compound semiconductor material. The second compound semiconductor material comprises a different material than the first compound semiconductor material such that the first compound semiconductor material has a two-dimensional electron gas (2DEG). The semiconductor device further includes a buried field plate disposed in the first compound semiconductor material and electrically connected to a terminal of the semiconductor device. The 2DEG is interposed between the buried field plate and the second compound semiconductor material.