Disclosed is a thin film transistor substrate which facilitates to improve output and transfer characteristics of thin film transistor, wherein the thin film transistor substrate comprises a thin film transistor comprising a lower gate electrode on a substrate, an active layer on the lower gate electrode, source and drain electrodes on the active layer, and an upper gate electrode on the source electrode, drain electrode and active layer, the upper gate electrode for covering a channel region defined by the source and drain electrodes; and a contact portion for electrically connecting the lower gate electrode with the upper gate electrode.