Radical species produced in Cat-CVD (hot-wire CVD) processes using SiH4 were identified by employing laser spectroscopic and mass spectrometric techniques. The major product of the cracking reaction of SiH4 on the heated tungsten surfaces is atomic silicon. The direct production of SiH and SiH3 radicals is minor. Under practical deposition conditions, such as in the presence of 1.0 Pa of SiH, and 5.7 Pa of H-2, Si atoms formed on the catalyzer surfaces react with SiH4 to produce silylsilylene, H3SiSiH, which may isomerize to disilene, H2Si=SiH2. In the presence of H-2, SiH3 radicals are produced efficiently in the H+SiH4 reaction. SiH3, as well as Si2H4, contributes to the film deposition.