Abstract: A polymeric resist mask composition thinly coated on a semiconductor substrate, wherein the prescribed portions of said resist mask are exposed to high energy rays such as electron beams, X-rays or ultraviolet rays for degradation, and the degraded portions of the resist mask are removed by an organic solvent to present a prescribed resist mask pattern on the semiconductor substrate, which comprises a halogenated polymethacrylic ester whose composition is expressed by the general formula ##STR1## (WHERE R denotes a halogenated alkyl radical including a halogen element selected from the group consisting of fluorine, chlorine and bromine, and at least one fluorine atom in case said radical contains chlorine or bromine and n indicates an average polymerization degree of 100 to 20,000) and an organic solvent for said halogenated polymethacrylate.