The present invention provides a chemically amplified positive resist
composition comprising (i) a polymer which is insoluble or poorly soluble
in an alkali aqueous solution but becomes soluble in an alkali aqueous
solution by the action of an acid, (ii) an acid generator, and (iii) a
compound of the formula (I). The present invention also provides an
ester derivative useful as a component of the chemically amplified
positive resist composition, and process for producing the ester
derivative.