The present paper describes a novel class of ketal-protected chemically amplified photoresists. Poly(1,4-dioxaspiro[4.4]nonane-2-methyl methacrylate) (poly(DNMMA)) was synthesized and evaluated as a matrix polymer. The ketal group of the polymer hydrolyzes under acid cataIysis to give two alcohol functionalities and a cyclopentanone. The ketal polymer is insoluble in an aqueous developer, while the hydrolyzed products are soluble. The decomposition temperature in the presence of acid was below room temperature. The polymer has high transparency in the deep UV region and its absorbances were 0.015 mu m(-1) at 248 nm and 0.163 mu m(-1) at 193 nm. The existence of the generated cyclopentanone after deprotection improves sensitivity by increasing acid diffusion.