We have deposited amorphous silicon thin films from monosilane (SiH4) gas by photochemical vapor deposition using a vacuum ultraviolet excimer lamp (VUV-CVD). We used an argon excimer lamp (λ=126 nm, hν=9.8 eV) whose photons are strongly absorbed by SiH4 gas. The substrate temperatures were changed from 25 to 300°C. When the temperature was lower than 150°C, the films included H–Si–H units and H2 molecules in its structure. When it was higher than 150°C, the main structural unit was Si–H.