A nitride compound semiconductor has a substrate and a nitride compound semiconductor stack on the substrate. The nitride compound semiconductor stack includes a multilayer buffer layer, a channel layer on this multilayer buffer layer, and an electron supply layer on this channel layer. A recess extends from the surface of the electron supply layer through the channel layer and the multilayer buffer layer. A heat dissipation layer in this recess is contiguous to the multilayer buffer layer and the channel layer and has a higher thermal conductivity than the multilayer buffer layer.