A carboxylic acid sulfonium salt having formula (1) is provided wherein R0 is hydrogen or a monovalent hydrocarbon group, R01 and R02 are hydrogen or a monovalent hydrocarbon group, at least one of R0, R01, and R02 has a cyclic structure, L is a single bond or forms an ester, sulfonate, carbonate or carbamate bond with the vicinal oxygen atom, R2, R3 and R4 are monovalent hydrocarbon groups. The sulfonium salt functions as a quencher in a resist composition, enabling to form a pattern of good profile with minimal LWR, rectangularity, and high resolution.