A positive resist composition for immersion exposure which comprises (A) a resin which enhances its solubility in an alkaline developer by the action of an acid and (B) at least one compound which generates an acid upon irradiation with an actinic ray or a radiation, the compound being selected from the following (Ba) to (Bc): (Ba) a sulfonium salt compound having a specific alkyl or cycloalkyl residue in the cation part, (Bb) a sulfonium salt compound having a specific alkyl or cycloalkyl residue in the cation part, and (Bc) a sulfonium salt compound having a specific alkyl or cycloalkyl residue in the anion part; and a method of pattern formation with the composition.