A thin film transistor includes a substrate; a gate electrode on the substrate; a gate insulating layer covering the gate electrode; a semiconductor layer corresponding to the gate electrode on the gate insulating layer; a protective layer covering the semiconductor layer and the gate insulating layer and having a source contact hole and a drain contact hole exposing a portion of the semiconductor layer; and a source electrode and a drain electrode on the protective layer and coupled to the semiconductor layer through the source contact hole and the drain contact hole, respectively, wherein the semiconductor layer has a source offset groove at a portion corresponding to the source contact hole of the protective layer.