Abstract: A semiconductor device provided with a thin-film transistor comprising a polycrystalline semiconductor thin film (2) formed on an insulating substrate (100). The semiconductor device comprises a channel region (80), a source region (91), and a drain region (92), each disposed on both sides of the channel region (80) in the semiconductor thin film (100). The channel region (90) comprises both a first conductive impurity and a second conductive impurity, the conductive type of the second conductive impurity being opposite the conductive type of the first conductive impurity, and is structured by layering a first layer in which the first conductive impurity and the second conductive impurity are canceled and a second layer in which either of the first conductive impurity or the second conductive impurity is dominant, wherein a gate electrode (4) is formed so as to face the first layer (2a) via an insulating film (3).