Alkali-developable, chemically amplified resist composition which comprises an alkali-insoluble compound having a structural unit containing a protected alkali-soluble group in which unit a protective moiety of said protected alkali-soluble group contains an alicyclic hydrocarbon group having bonded to a carbon atom thereof a —CH2—R1′ group wherein R1′ is methyl, ethyl, propyl or isopropyl, and said alkali-soluble group is cleaved upon action of an acid generated from a photoacid generator used in combination with said compound, thereby releasing said protective moiety from the alkali-soluble group and converting said compound to an alkali-soluble one, and a photoacid generator capable of being decomposed upon exposure to a patterning radiation to thereby produce an acid capable of causing cleavage of said protective moiety. The resist composition can exhibit a high sensitivity (not more than 5 mJ/cm2) and therefore is particularly suitable for ArF lithography and also can exhibit stable patterning properties.