A radiation sensitive resin composition comprising (A) a copolymer possessing recurring units of the formulas (1), (2), and (3), which turns alkali soluble in the presence of acid and (B) a photosensitive acid generator. Because the composition can resolve line-and-space patterns, isolated patterns, and contact hole patterns with satisfactory appearance and high resolution, it is useful as a chemically amplified positive resist for use in the manufacture of semiconductor devices.