Positive-working photoresist composition

A chemical-amplification positive-working photoresist composition which comprises, as a uniform solution in an organic solvent:

• (A) a polyhydroxystyrene-based resinous ingredient of which the hydroxyl groups are partly substituted by acid-dissociable substituent groups capable of being dissociated by interacting with an acid;
• and
• (B) a radiation-sensitive acid-generating compound capable of releasing an acid by irradiation with a radiation, the resinous ingredient as the component (A) being a combination comprising (A1) a first polyhydroxystyrene resin substituted for a part of the hydroxyl groups by acid-dissociable substituent groups and (A2) a second polyhydroxy-styrene resin substituted for a part of the hydroxyl groups by acid-dissociable substituent groups which are the same as in the first polyhydroxystyrene resin (A1), of which the degree of substitution by the substituent groups for a part of the hydroxyl groups in the first polyhydroxystyrene resin (A1) is larger than the degree of substitution in the second polyhydroxystyrene resin (A2) with the proviso that the ratio of the maximum weight-average molecular weight Mwmax to the minimum weight-average molecular weight Mwmin in the first and second polyhydroxystyrene resins (A1) and (A2) is smaller than 1.5.