A thin film transistor and a method of manufacturing the thin film transistor is disclosed. The thin film transistor includes first and second ohmic contact layers, an activation layer, an insulating layer, a source electrode formed on the insulating layer and connected to the first ohmic contact layer through first contact hole, a drain electrode formed on the insulating layer and connected to the second ohmic contact layer through second contact hole, a gate electrode formed on the insulating layer between the source electrode and the drain electrode and overlapping the activation layer, and a protective layer formed on the source electrode, the drain electrode, and the gate electrode.