PURPOSE: To reduce the width of an isolation and diffusion layer and increase the thickness and the strength of a chip when producing a plurality of thyristor chips from a large-sized wafer.

CONSTITUTION: An isolation and diffusion layer 2 is installed to one of an N type semiconductor substrate. This side is mirror-polished. One side of a P type semiconductor substrate 4 is mirror-polished so that it may be bonded with the aforesaid mirror surface. They are heat-treated, thereby finishing their junction. The surface of the N type semiconductor substrate 1 is abraded, thereby forming an isolation and diffusion layer 6, a gate 7 and the like.