ABSTRACTTwo organosilicon molecules tetraethysilane (TESi) and tetravinylsilane (TVSi) were used to prepare thin films of silicon carbide by chemical vapor deposition (C. V. D.). In each of the molecule, the ratio C/Si = 8, the only difference between TESi and TVSi is the structure of the radicals ethyl (.CH2-CH3) and vinyl (.CH=CH2). This feature induces different thermal behavior and leads to the formation of different materials depending on the nature of the carrier gas He or H2· The decomposition gases are correlated with the material deposited which is investigated by I.R. and Raman spectroscopy. The structure of the starting molecule influences the mechanisms of decomposition and consequently the structure of the material obtained.