JPH05235054

PURPOSE:To improve a mutual conductance while a noise factor at the time of the high-frequency operation of a field-effect semiconductor device is suppressed low by a method wherein a channel layer is formed into a laminated structure consisting of an undoped InGaAs layer, an n-type InGaAs layer and an undoped InGaAs layer. CONSTITUTION:A buffer layer 2 is provided on a semi-insulative GaAs substrate 1 and moreover, a channel layer 10 is provided. This channel layer 10 consists of a layer 10a constituted of an undoped InGaAs semiconductor layer having an electron affinity larger than that of a GaAs semiconductor layer constituting the layer 2, a layer 10b consisting of an n-type InGaAs semiconductor layer, which has the electron affinity larger than that of the GaAs semiconductor layer constituting the layer 2 and is doped with an n-type impurity in a high concentration, and an undoped InGaAs layer 10c having the electron affinity larger than that of the GaAs semiconductor layer constituting the layer 2. Thereby, electrons in a channel at the time of operation of an element are brought in a first excited state and the probability of the existence of the electrons is small in the n-type InGaAs layer 10b and is increased in the undopd InGaAs layers 10 and 10c.