A positive resist composition is provided comprising (A) a resin comprising recurring units having adamantane ring and recurring units having cyclopentyl so that the resin may increase its alkali solubility under the action of acid, (B) a mixture of sulfonium salts, and (C) a solvent. By coating the resist composition as a resist film, forming a protective film thereon, and effecting immersion lithography, a pattern of good profile is formed at a high resolution.