A sulfonium salt compound excelling in transparency to deep ultraviolet rays at a wavelength of 220 nm or less, exhibiting well-balanced excellent performance such as sensitivity, resolution, pattern form, LER, and storage stability when used as a photoacid generator, a photoacid generator comprising the sulfonium salt compound, and a positive-tone radiation-sensitive resin composition containing the photoacid generator. The sulfonium salt compound is shown by the following formula (I), wherein R.sup.1 represents a halogen atom, an alkyl group, a monovalent alicyclic hydrocarbon group, an alkoxyl group, or --OR.sup.3 group, wherein R.sup.3 is a monovalent alicyclic hydrocarbon group, R.sup.2 represents a (substituted)-alkyl group or two or more R.sup.2 groups form a cyclic structure, p is 0-7, q is 0-6, n is 0-3, and X.sup.- indicates a sulfonic acid anion. The positive-tone radiation-sensitive resin composition comprises (A) a photoacid generator of the sulfonium-salt compound and (B) an acid-dissociable group-containing resin.