A thin film transistor includes a gate electrode, a semiconductor layer, a source electrode, a drain electrode, a first protective layer, and a second protective layer. The gate electrode is disposed on a substrate. The metal oxide semiconductor layer is disposed on a gate insulating layer and electrically connects the source electrode and the drain electrode. The first protective layer disposed on the metal oxide semiconductor layer has a first oxygen vacancy concentration. The second protective layer disposed on the first protective layer has a second oxygen vacancy concentration. A boundary area located between the first and second protective layers has a third oxygen vacancy concentration. The third oxygen vacancy concentration is respectively greater than the first oxygen vacancy concentration and the second oxygen vacancy concentration.