PURPOSE: To suppress a short channel effect by covering a whole semiconductor substrate with a thin insulating film having small impurity diffusion, removing part of the thin film, forming a thin metal film which becomes an impurity diffusion source on the whole substrate, and thermally annealing it.

CONSTITUTION: A thermal oxide film 7 is formed on a whole substrate by oxidizing the substrate in an oxygen atmosphere. Then, an N-channel transistor region is covered with a resist, the oxide film of a P-channel transistor is removed, and the resist is then exfoliated. Thereafter, a thin metal boron film 8 is formed on the substrate, and annealed to form a P+ type layer. Subsequently, after the remaining film 8 is converted into a BSG, it is removed by etching. Then, after an SiO2 film 10 is deposited on the whole substrate, an aluminum film is deposited, and patterned to form wirings 11. That is, the N-channel transistor region is covered with the film 7, and the film 8 is diffused as an impurity diffusion source to form a very shallow P+ type junction. Accordingly, a decrease in a gate threshold value voltage is reduced, and a short channel effect is remarkably suppressed.