FIELD-EFFECT TRANSISTOR

PURPOSE:To inhibit a scattering of impurities and to improve the mutual conductance of a field-effect transistor by a method wherein carrier feeding layers consisting of the same semiconductor layer are respectively provided on and under a carrier transit layer of the field-effect transistor or a carrier feeding layer consisting of a semiconductor layer is provided on the carrier transit layer and the impurity concentration in the carrier transit layer, which is an active layer, is reduced. CONSTITUTION:In a field-effect transistor, carrier feeding layers 4 and 6, which are the same semiconductor layer, consist of the same conductivity type and have an impurity concentration higher than that in a carrier transit layer 5, are respectively provided on and under the layer 5. Thereby, the N-type GaAs carrier transit layer 5 is formed into a region having a high electron concentration and the N-type GaAs electron carrier feeding layer 4 having the high impurity concentration and the N-type GaAs electron carrier feeding layer 6 having the high impurity concentration are respectively formed into a region having an electron concentration which is changed by a gate electric field and a substrate electric field. As the regions depleted by the gate electric field and the substrate electric field are formed into the layers having the high impurity concentration, the impurity concentration in the layer 5 can be set low and a transistor having a high mutual conductance is obtained at a high mobility.