Method of suppressing diffusion in a semiconductor device

An impurity-diffused layer having an extension structure is formed first by implanting Sb ion as an impurity for forming a pocket region; then by implanting N as a diffusion-suppressive substance so as to produce two peaks in the vicinity of the interface with a gate electrode and at an amorphous/crystal interface which serves as an defect interface generated by the impurity in the pocket region; and by carrying out ion implantations for forming an extension region and deep source and drain regions.