A chemical amplification positive resist composition comprising a polymeric mixture of a polyhydroxystyrene derivative having a Mw of 1000-500,000 and a copolymer of hydroxystyrene and (meth)acrylate having a Mw of 1000-500,000, as a base resin, has improved dry etching resistance, high sensitivity, high resolution, and process adaptability, and is suppressed in the slimming of pattern films after development with aqueous base.