A method of etching a polysilicon film specimen by an electronic cyclotron resonance etching technique or a microwave plasma etching technique includes the first process in which a mixed gas containing Cl.sub.2 and HBr is used as a process gas for etching, the Cl.sub.2 occupying 50-70 vol. % of the whole mixed gas; and the second process in which a mixed gas containing HBr and He is used, with HBr being in a proportion of 20-50 vol. % of the mixed gas, and a low bias voltage from -100 to -30 volts is applied to a specimen carrier. Further, in the first and second processes, a mixed gas containing HBr and He is used, with HBr being in a proportion of 20-50 vol. %, and a relatively high bias voltage from -250 to -100 volts is applied to the specimen carrier in the first process, while a low bias voltage from -100 to -30 volts is applied to the same in the second process. According to the present invention, a polysilicon film can be etched without causing undercut and with high dimensional accuracy.