PURPOSE: To reduce the quantity of Si or the like being diffused, as an impurity, into a channel layer by performing the epitaxial growth at a specific temperature and ending the growth of a final electrode layer within a specific time after formation of a planar dope layer.

CONSTITUTION: After forming a channel layer 2 of GaAs and a spacer layer 3 of AlGaAs on a GaAs substrate 1, Si or the like is planar doped to form an AlGaAs layer 5 and an electrode layer 6 of Si doped GaAs. Epitaxial growth is then effected by MOCVD under normal pressure in the temperature range of 620-660°. After planar doping, the growth rate is varied by varying the material supply and the growth is ended within 180sec. The temperature is lowered quickly upon finish of growth. Since the growing time after planar doping is limited to a short time, the time of high temperature diffusion is shortened and thereby the diffusion distance is shortened. Consequently, the quantity of Si or the like being diffused up to the channel layer can be reduced.