Photoresist composition

A photoresist composition comprising a resin which comprises a structural unit represented by the formula (I):

• wherein Q1 and Q2 independently represent a fluorine atom or a C1-C6 perfluoroalkyl group, U represents a C1-C20 divalent hydrocarbon group in which one or more —CH2— may be replaced by —O—, —NH—, —S—, —NRc—, —CO— or —CO—O—, Rc represents a C1-C6 alkyl group, X1 represents —O—CO—, —CO—O—, —CO—O—CH2—, —CH2—O—CO—, —O—CH2—, —CH2—O—, —NRd—CO— or —CO—NRd—, Rd represents a hydrogen atom or a C1-C6 alkyl group, and A+ represents an organic counter ion, and a compound represented by the formula (D):
• wherein R1, R2, R3 and R4 independently represent a C1-C8 alkyl group, and A1 represents a C3-C36 divalent saturated cyclic hydrocarbon group which can contain one or more heteroatoms and which have one or more substituents or a C6-C20 divalent aromatic hydrocarbon group which can contain one or more heteroatoms and which have one or more substituents.