The effects of hydrogenated microcrystalline silicon (mu c-Si:H) film with various crystalline factors on thin-film transistors (TFTs) with low-high-low band gap structure are studied. Compared to hydrogenated amorphous silicon (a-Si:H) TFT with conventional inverted-stagger structure, the device with mu c-Si:H film of high crystalline factor in the active channel depicts improved interfacial active layer near the gate insulator interface as well as the later-grown bulk active layer, resulting in improved device parameters including field effect mobility, threshold voltage, subthreshold swing and ON-current. While a-Si:H film of low crystalline factor and high-band-gap is proposed for the source and drain offset regions in the new device to prevent the band-to-band tunneling, thus alleviates the high OFF-current inherent in conventional mu c-Si:H thin-film transistors, resulting in an improved ON/OFF current ratio.