The infralow‐pressure chemical vapor deposition (ILPCVD) system has been developed to reduce the partial pressure of silane (PSiH4) to the sub‐mTorr order by increasing the pumping speed, while aiming at the improvement of as‐deposited polycrystalline silicon (poly‐Si) film qualities. The films prepared by the system show better physical properties than ordinary low‐pressure chemical vapor deposition (LPCVD) films at fixed temperature (600 °C), so that the low‐temperature processed as‐deposited poly‐Si thin film transistors can be easily and significantly improved, having ON/OFF current ratios of more than 108. Physical analyses have confirmed that the films deposited at temperatures as low as 555 °C by the ILPCVD system are undoubtedly polycrystalline. The fabrication of poly‐Si TFT’s through a low‐temperature process confirms good semiconductive behavior of the films, even when deposited at 555 °C. The superiority of the ILPCVD over other LPCVD’s is explained by the deposition kinetics. The nature of LPCVD as‐deposited polysilicon film is characterized by the competition between surface reaction rate and gas‐phase mass‐transfer rate. High‐temperature or infralow‐pressure deposition is controlled by gas‐phase mass transfer of the reactant. The mass‐transfer controlled deposition is found to be preferable to obtaining good polycrystalline silicon film, namely high crystallinity, ⟨100⟩ preferred orientation, large grains, and good semiconductive properties.