Phenylsilane, SiH3, subjected to a low power rf discharge at low pressures and elevated temperatures results in polymeric films of unusual properties. In contrast to the known plasma chemistry of other aromatic materials, the benzene ring of SiH3 does not fragment in the plasma polymerization process as is indicated by the virtual absence of aliphatic C-H stretching frequencies in the infrared spectrum of the deposited film. A similar lack of aliphatic hydrogen is observed in plasma polymers from diphenylsilane, disilylbenzene, and p-chlorophenylsilane. The predominant structural features of the phenylsilane plasma polymer films are cross-linked polysilane chains with pendant phenyl groups. The degree of cross-linking increases with increasing substrate temperature. The films are resistant to thermal degradation in vacuo to 500°C and maintain their mechanical integrity during thermal oxidation in air. © 1982, The Electrochemical Society, Inc. All rights reserved.