PURPOSE: To stop side etching as well as to contrive to be able to protect parts, which are used as a source region and a drain region, of an active region by a method wherein an insulating film, on which an opening part is opened, is formed on a semiconductor substrate, wherein the active region is formed, and a gate region is formed on the active region through the opening part using the insulating film as a mask and the like.

CONSTITUTION: An insulating film 3, which has electrical insulating properties and has an opening part 4 opened at a prescribed position on an active region 2, is formed on a semiconductor substrate 1, wherein the active region 2 is formed, and a gate region 5 is formed on the active region 2 through the opening part 4 using the insulating film 3 as a mask. Then, a gate electrode 6a is formed on the opening part 4, an impurity for a source region and an impurity for a drain region are respectively implanted in the active region 2 excluding the gate electrode 5 using the gate electrode 6a as a mask and the source region 8 and the drain region 9 are formed. For example, Si ions are implanted in the GaAs substrate 1 to form the active region 2 and the Si3N4 insulating film 3 is formed. Zn is thermodiffused through the opening part 4 to form the gate region 5 and the gate electrode 6a consisting of WSix is formed.