The present invention provides a chemically amplified positive resist composition comprising (A) a resin which comprises (i) at least one structural unit selected from the group consisting of structural units of the formulas (no and (V), (ii) a structural unit of the formula (I) and (iii) a structural unit of the formula (II), and (B) an acid generator.The present invention also provides a haloester derivative of the formula (XXI) and a process for producing the same ##STR00001##