Transport mechanism of deposition precursors in catalytic chemical vapor deposition (CVD) often called hot-wire CVD, was investigated to identify the precursor species and make the conditions for uniform-film preparation known. Precursor-transport mechanism was analysed from the film-thickness profiles of amorphous silicon in the reactor tube as a function of the distance from the catalyzer. It was found that precursors are mainly transported by thermal diffusion. However, the affect of the gas flow on precursor transport was effective at a pressure of a few tens Pa and gas-flow velocity faster than several m/s. Decomposition probability of one SiH4 molecule by one collision with the catalyzer is estimated to be about 40%. Efficiency of gas use for SiH4 was several tens % because of high decomposition probability of SiH4. (C) 2000 Elsevier Science B.V. All rights reserved.