High electron mobility transistor having thin, low resistance schottky contact layer

A high electron mobility transistor has a double-heterojunction structure including a channel layer for developing therein an electron gas layer having a substantially uniform electron gas density, and upper and lower high-resistance wide-band gap layers disposed respectively over and beneath the channel layer. Each of the upper and lower high-resistance wide-band gap layers has a silicon-doped planar layer disposed therein. The upper high-resistance wide-band gap layer including a low-resistance wide-band gap layer disposed in an upper end region thereof remotely from the channel layer.