A chemically amplified positive resist composition is provided comprising (A) a resin containing acid labile groups other than acetal type which changes its solubility in an alkaline developer as a result of the acid labile groups being eliminated under the action of acid and (B) specific sulfonium salts as a photoacid generator. The composition is improved in resolution and focus latitude, minimized in line width variation and profile degradation even on prolonged PED, improved in pattern profile after development, minimized in pattern feature size variation within the wafer plane by uneven development and thus best suited in the deep-UV lithography.