PURPOSE: To improve the reproducibility and contrive to reduce contact resistance by a method wherein ion implantation is performed prior to the process of alloying diffusion of an ohmic metal, so as to produce a large amount of lattice defect to the neighborhood of the position of the existence of an already formed channel.

CONSTITUTION: A recess 4A is formed at a gate electrode forming scheduled part. An Si dioxide (SiO2) film 5 is formed and patterned, and the part covering the recess 4A is left, then removing the other part. By adapting ion implantation method, an ion 6 an N type impurity is selectively implanted with the Si dioxide film 5 as a mask. After removing the Si dioxide film 5 used as the mask, a source electrode 8S and a drain electrode 8D are formed. For alloying, heat treatment is performed, and a gate electrode 9 is formed, thus completing the device. Thereby, the impurity is diffused uniformly and deeply, therefore an alloying contact of a low resistance and a high uniformity can be obtained with good reproducibility.