A chemically amplified photoresist composition comprising, (a) a compound which cures upon the action of an acid or a compound whose solubility is increased upon the action of an acid; and (b) as photosensitive acid donor, at least one compound of the formula Ia, Ib, Ic, IIb or IIc wherein R₁ is for example C₁-C₅alkyl, C₃-C₃₀cycloalkyl, C₁-C₅haloalkyl, C₂-C₁₂alkenyl, C₄-C₈cycloalkenyl, C₆-C₁₂bicycloalkenyl, phenyl, naphthyl, anthracyl, phenanthryl, or is a heteroaryl radical; all of which are unsubstituted or substituted; optionally some of the substituents form 5- or 6-membered rings with further substituents on the phenyl, naphthyl, anthracyl, phenanthryl, or heteroaryl ring or with one of the carbon atoms of the phenyl, naphtyl, anthracyl, phenanthryl, or heteroaryl ring; R₁ is for example C₁-C₁₂alkylene, C₃-C₃₀cycloalkylene, phenylene, naphtylene, diphenylene, or oxydiphenylene, wherein these radicals are unsubstituted or substituted; A and B for example are a direct bond; Ar₁ and Ar₂ independently of each other for example are phenyl, naphtyl, anthracyl, phenanthryl, or heteroaryl, all of which are unsubstituted or are substituted; Ar₃, Ar₄ and Ar₅ for example have one of the meanings given for Ar₁ and Ar₂; Y is for example C₃-C₃-C₃₀cycloalkylene, phenylene, naphthylene, diphenylene, or oxydiphenylene, all of which are unsubstituted or substituted.