A self-aligned top-gate thin film transistor (TFT) and a method of forming such a thin film transistor, by forming a semiconductor thin film layer; printing a doped glass pattern thereon, a gap in the doped glass pattern defining a channel region of the TFT; forming a gate electrode on or over the channel region, the gate electrode comprising a gate dielectric film and a gate conductor thereon; and diffusing a dopant from the doped glass pattern into the semiconductor thin film layer.