A photoacid generator represented by Formula 1 or Formula 2: wherein R1, R2, and R3 are each independently a C1-C10 alkyl group, X is a C3-C20 alicyclic hydrocarbon group forming a ring with S+, and at least one CH2 group in the alicyclic hydrocarbon group may be replaced with at least one selected from the group consisting of S, O, NH, a carbonyl group, and R5—S+A−, where R5 is a C1-C10 alkyl group, and A− is a counter-ion.