An inverted stagger thin film transistor includes an insulating substrate, a silicon active layer formed thereon, source and drain ohmic contact layers, source and drain electrodes respectively contacting the source and drain ohmic contact layers, and a gate electrode opposite to the channel region of the active layer through a gate insulating film. An auxiliary film consisting of a silicon film doped with nitrogen is formed in the surface of the active layer, and the ohmic contact layers contact the auxiliary film. The auxiliary film can be continuously formed from the active layer to the ohmic contact layers, thereby improving a junction state between the active layer and the ohmic contact layers.