Manufacturing process of thin film transistor

A thin film transistor includes a gate, a gate insulator layer, a channel layer, a source, a drain, and an ohmic contact layer. The gate insulator layer covers the gate; the channel layer is disposed on the gate insulator layer above the gate; the source and the drain are disposed on the channel layer; the ohmic contact layer is disposed between the channel layer and the source and drain. The ohmic contact layer is constituted by a number of film layers. As mentioned above, the thin film transistor has an ohmic contact layer constituted by a number of film layers. When the thin film transistor is turned off, the current leakage thereof is lowered than that of a conventional thin film transistor.