PURPOSE: To block the transverse directional diffusion advancing downward of a gate from a source and a drain region and then inhibit punch through by boring a groove in the semiconductor layer between the source and the drain regions constituting an FET, and forming a gate electrode therein via an insulation layer.

CONSTITUTION: Thick insulation oxide film 2 serving as the gate region and element isolation regions are formed by selective oxidation on the surface of a semiconductor substrate 1, and the film 2 of the gate region positioned at the center is removed by etching, thus generating the deep groove therein. Next, a thin insulation oxide film 3 for gate is adhered over the entire surface including said groove, and, by being positioned thereon, the gate electrode 4 composed of polycrystalline Si is formed on the groove. Thereafter, impurity ions are implanted through the film 3 positioned on both sides of said electrode, and accordingly the source and drain regions 5 are generated on the surface layer of the substrate 1 by self-alignment. Thus, the transverse directional diffusion of the region 5 is blocked, and at the same time the generation of punch through is eliminated.