A thin film transistor array substrate includes a gate line disposed on a substrate, the gate line comprising a gate electrode including a lower film and an upper film thicker than the lower film, a gate insulating layer formed on the gate line, a semiconductor layer formed on the gate insulating layer, an ohmic contact layer formed on the semiconductor layer, a data line electrically connected to a source electrode and a drain electrode formed on the ohmic contact layer, the lower film of the gate line is in contact with the gate insulating layer at a crossing portion of the gate line and the data line and the heights of the source electrode and the drain electrode are substantially the same as or less than a height of the semiconductor layer.