Disclosed is a novel positive-working or negative-working chemical-sensitization photoresist composition useful in the photolithographic patterning works for the manufacture of electronic devices. The photoresist composition is characterized by a unique acid-generating agent capable of releasing an acid by the pattern-wise exposure of the resist layer to actinic rays so as to increase or decrease the solubility of the resist layer in an aqueous alkaline developer solution. The acid-generating agent proposed is a novel cyano group-containing oxime sulfonate di- or triester compound represented by the general formulaA�C(CN).dbd.N--O--SO.sub.2 --R!.sub.n,in which each R is, independently from the others, an unsubstituted or substituted monovalent hydrocarbon group such as alkyl groups, A is a divalent or tervalent organic group or, preferably, phenylene group and the subscript n is 2, when A is a divalent group, or 3, when A is a tervalent group or, preferably 2. Since more than one of sulfonic acid molecules are released from one molecule of the sulfonate compound by the exposure to actinic rays, the chemical-sensitization photoresist composition exhibits high photosensitivity.