PURPOSE: To prevent silicon from being undercut during etching with gas plasma and to attain an enhanced yield by using a gaseous mixture contg. a prescribed amount of H2 and ≥1 kind of gas such as CCl4, CCl3F or CCl2F2.

CONSTITUTION: Silicon 6 is mounted on a smaple electrode 2 in a reaction chamber 1, and the chamber 1 is evacuated. A small amount of a reactive gas contg. 15W50% H2 and ≥1 kind of gas selected from CCl4, CCl3F, CCl2F2, CClF3 and CF4 is fed into the chamber 1. It is then exhausted to maintain the chamber 1 at a certain vacuum degree. By applying a high frequency voltage between the electrode 2 and a counter electrode 3 facing to the electrode 2, the silicon 6 is etched. By this method the etched pattern of the silicon undergoes no undercutting, and an enhanced yield is attained.