Silicon-containing polymers comprising recurring units of formula (1) are novel wherein R1 is a single bond or alkylene, R2 is hydrogen or alkyl, R3, R4 and R5 are alkyl, haloalkyl, aryl or silicon-containing group, R6 is hydrogen, methyl, cyano or —C(═O)OR8 wherein R8 is hydrogen, alkyl or acid labile group, R7 is alkyl, —NR9R10 or —OR11 wherein R9, R10 and R11 are hydrogen or alkyl, a and b are positive numbers satisfying 0<a+b≦1. Resist compositions comprising the polymers are sensitive to high-energy radiation and have a high sensitivity and resolution at a wavelength of less than 300 nm and improved resistance to oxygen plasma etching.