Microcrystalline silicon films were deposited by diluted-hydrogen method and hydrogen-atom-treatment method at 250 o C in a plasma enhanced chemical vapor deposition system and they were characterized by nuclear magnetic resonance, Raman spectroscopy, and optical bandgap measurements. One-mask a-Si:H thin film transistors (TFT's) were fabricated with those microcrystalline materials as the channel layer. The highest electron mobilities of the TFT's fabricated by diluted-hydrogen method and hydrogen-atom-treatment method were 1.23 and 1.04 cm 2 /V.s, respectively without any' thermal treatment steps