A thin film transistor, a method of manufacturing the thin film transistor, and a display device including the thin film transistor are provided. The thin film transistor comprises a gate electrode formed on the oxide semiconductor layer such that a first surface of the oxide semiconductor layer faces the gate electrode. A source electrode and a drain electrode are electrically connected to the oxide semiconductor layer, respectively. The oxide semiconductor layer, gate electrode, source electrode and drain electrode are arranged in a coplanar transistor configuration. A light-blocking element is also arranged to shield a second surface of the oxide semiconductor layer from external light.