In a heterostructure field effect transistor (MISHFET), a source ohmic
electrode 105 and a drain ohmic electrode 106 are formed on an AlGaN
barrier layer 104. A SiNx gate insulator 108, a p-type polycrystalline
SiC layer 109, and a Pt/Au gate electrode 110 being an ohmic electrode
are formed one on another on the AlGaN barrier layer 104. Since the
p-type polycrystalline SiC layer 109 is relatively large in work
function, the channel of the MISHFET is depleted even in its zero-bias
state, so that the normally-OFF operation occurs.