A photo-decomposable compound, a photoresist composition including the photo-decomposable compound, and a method of manufacturing an integrated circuit (IC) device using the photoresist composition, the photo-decomposable compound including a phenyl sulfonium cation component; and an anion component, wherein the phenyl sulfonium cation component has a protecting group, which is decomposable by an action of acid to generate an alkali-soluble group in response to exposure, the anion component generates acid in response to exposure, the protecting group is represented by *—C(═O)OR, in which R is a substituted or unsubstituted t-butyl group or a substituted or unsubstituted C3 to C30 alicyclic group, and * is a bonding site, and the protecting group is bonded to a phenyl group of the phenyl sulfonium cation component through an ether linking group.