A thin film transistor disposed on a substrate is provided. The thin film transistor includes a gate, a gate insulating layer, a silicon-rich channel layer, a source, and a drain. The gate is disposed on the substrate. The gate insulator is disposed over the gate. The silicon-rich channel layer is disposed above the gate, wherein the material of the silicon-rich channel layer is selected from a group consisting of silicon-rich silicon oxide (Si-rich SiOx), silicon-rich silicon nitride (Si-rich SiNx), silicon-rich silicon oxynitride (Si-rich SiOxNy), silicon-rich silicon carbide (Si-rich SiC) and silicon-rich silicon oxycarbide (Si-rich SiOC). The content (concentration) of silicon of the silicon-rich channel layer within a film depth between 10 nm to 170 nm ranges from about 1E23 atoms/cm3 to about 4E23 atoms/cm3. The source and the drain are connected with the silicon-rich channel layer.