Thin films of poly(dimethylsilane) (PDMS) and permethyldodecasilane (DM12) were prepared by the vacuum-deposition method, and the molecular orientation in the films was investigated. Well-oriented films of DM12 were prepared without detectable degradation; however, degradation occurred in the films of PDMS, though well-oriented films were also obtained. Infrared and UV spectra of the vacuum-deposited films were measured with inclined sample alignment. In the spectra of films deposited to substrates at room temperature, a methyl rocking (parallel) band and a sharp UV absorption, which have the same polarity parallel to the chain axis, became stronger when the samples were inclined. Both of the absorptions also showed large dichroism when the samples were inclined. These results suggest that the PDMS and DM12 molecules in the films were oriented perpendicular to the substrate. The infrared spectra of vacuum-deposited PDMS films show Si-H and Si-O bonds formation; i.e., PDMS molecules were degraded during the deposition process. In clear contrast, the infrared spectra of the vacuum-deposited films of DM12 showed no molecular degradation.