Resist compositions comprising as the base resin a polymer using tert-amyloxystyrene as a reactive group which is decomposable under the action of an acid to increase solubility in alkali have advantages including a significantly enhanced contrast of alkali dissolution rate before and after exposure, a high sensitivity, and a high resolution in the baking temperature range of 100-110 C. which is unachievable with tert-butoxystyrene. The compositions are best suited as a chemically amplified resist material for micropatterning in the manufacture of VLSI.