Patent ID: 8378387

Claim:
A field effect transistor, comprising: a nitride-based semiconductor multilayer structure, at least including, a drift layer formed of n-type or i-type AlxGa 1-X N(0≦X≦0.3), a barrier layer formed of i-type Al Y Ga 1-Y N (Y>X), an electron supply layer formed of n-type Al Y Ga 1-Y N, and a channel layer formed of i-type GaN or InGaN, that are epitaxially grown on a substrate in this order, from a side of the substrate, a suitable buffer layer being interposed between the substrate and the nitride-based semiconductor multilayer structure; a gate electrode formed in a part of a front surface of the channel layer with an insulating film interposed therebetween; an n + type connection region in which n-type impurities are doped with the density of 1×10 18 cm −3 or more, in a range from at least a part of a channel layer to a part of the drift layer, adjacent to one side in a planer direction of an area where the gate electrode is formed; a source electrode formed on a front surface of the nitride-based semiconductor multilayer structure in the opposite side of the n + type connection region with respect to the gate electrode; and a drain electrode formed on a back surface of the substrate.