ArF laser irradiation into gaseous trimethyl(propynyloxy)silane, trimethyl(ethenoxy)silane and trimethyl(ethynyl)silane results in chemical vapour deposition of thin films of solid organosilicon polymers. UV excitation of the two former compounds leads to polymerization at the triple bond as a major process to yield, respectively, saturated poly(trimethylsilyloxyhydrocarbon) and poly(trimethylsilylhydrocarbon), whereas that of the latter compound is controlled by cleavage reactions to afford poly(methylsiloxane). The processes represent a unique photopolymerization in the absence of photoinitiators.