A positive resist composition comprises (A) a resin component which becomes soluble in an alkaline developer under the action of an acid, and (B) an acid generator which is a specific sulfonium salt compound. The resin (A) is a polymer comprising tertiary alkyl protective group units having a hydrophobic tetracyclo[4.4.0.1.sup.2,5.1.sup.7,10]dodecane structure, di- or trihydroxyadamantyl units, and monocyclic lactone units.