Provided is a thin film transistor array substrate, including a gate electrode, a gate insulating layer covering the gate electrode, a semiconductor pattern formed on the gate insulating layer and including a channel region overlapping the gate electrode, a source electrode and a drain electrode formed on the semiconductor pattern and facing each other with a first opening exposing the channel region therebetween, a first protective layer formed on the gate insulating layer to cover the source electrode, the drain electrode and the semiconductor pattern and a metal oxide layer formed along a surface of the first protective layer.