Poly(2-trimethylsilyl-2-propyl methacrylate-co-gamma-butyrolactone-2-yl methacrylate) was synthesized and evaluated as a chemically amplified resist for ArF lithography. The polymer has excellent transmittance at 248 nm and also has a good transmittance at 193 nm. in addition, the polymer possesses good thermal stability up to 200 degrees C, whereas in the presence of an acid the cleavage of the 2-trimethylsilyl-2-propyl eater group begins at about 80 degrees C in a catalytic manner. Patterns of 0.24 mu m line/space were obtained with a conventional developer, 2.38 wt.% tetramethylammonium hydroxide aqueous solution, using an ArF excimer laser exposure system.