The invention provides a chemical-amplification positive-working photoresist composition suitable for forming a resist film of a relatively large thickness on a substrate in addition to other advantages. The inventive composition contains (A) a photoacid-generating agent, (B) an alkali-insoluble resin capable of being imparted with increased alkali-solubility by interaction with an acid, (C) an alkali-soluble resin and (D) an organic solvent, wherein the component (C) is (C1) a polyhydroxystyrene or a copolymer having at least 80% by mass of the hydroxystyrene units in an amount not exceeding 15 parts by mass relative to 100 parts by mass of the total amount of the components (B) and (C).