A growth mechanism diagnosis for high-rate, polycrystalline silicon deposition using hot-wire CVD is explored in this article. The effects of various deposition parameters on the Si film growth are investigated by Raman spectroscopy and transmission electron microscopy (TEM) measurements, with special attention paid to the crystalline and amorphous phases. It is found that the H 2 /SiH 4 ratio and substrate temperature (T s ) are the essential process parameters in determining the crystalline phase and the incubation thickness of the as-deposited Si film. Under low hydrogen dilution conditions, an amorphous incubation layer was formed and degraded the crystalline fraction of the Si film. The incubation thickness prior to the nucleation decreases with the increase of the hydrogen dilution ratio. Under higher H 2 /SiH 4 ratios (≥50), the amorphous phase deposited on the substrate could be etched selectively by the atomic hydrogen. As a consequence, nucleation of small crystallite occurs directly on the substrate. At low substrate temperatures, the deposition process shows the disadvantages of small grain size and low crystallinity. The poly-Si film can be deposited from the seed layer under high T s conditions (>350 °C) where the Si appears singly crystallized at the initial stage and then grows epitaxially.