In a positive resist composition comprising (A) a resin component which becomes soluble in an alkaline developer under the action of an acid and (B) a photoacid generator, component (A) is a polymer of formula (1) wherein R.sup.1 is H, methyl or trifluoromethyl, R.sup.2 and R.sup.3 are alkyl, R.sup.4 is a monovalent hydrocarbon group, X.sup.1 is O, S or CH.sub.2CH.sub.2, X.sup.2 is O, S, CH.sub.2 or CH.sub.2CH.sub.2, n is 1 or 2, a1, a2, c, d1 and d2 each are from 0 to less than 1, b is from 0.01 to less than 1, and a1+a2+b+c+d1+d2=1. The resist composition forms a pattern with high rectangularity at an enhanced resolution when processed by ArF lithography. ##STR00001##