A positive resist composition comprising (A) a polymer comprising recurring units of a specific structure adapted to generate an acid in response to high-energy radiation and acid labile units, the polymer having an alkali solubility that increases under the action of an acid, and (B) a sulfonium salt of a specific structure exhibits a high resolution in forming fine size patterns, typically trench patterns and hole patterns. Lithographic properties of profile, DOF and roughness are improved.