In a bottom gate-type thin-film transistor manufacturing method, after ion doping, an ion stopper (55) is removed. The ion stopper (55) does not remain in the interlayer insulating film (8) lying immediately above the gate electrode. The thin-film transistor has such a structure that no ion stopper (55), and the interlayer insulating layer is in direct contact with at least the channel region of the semiconductor layer (4). The impurity concentration in the vicinity of the interface between the interlayer insulating film and the semiconductor layer 4 is 10.sup.18 atoms/cc or less. This structure can prevent the back channel phenomenon and reduce variations in characteristic resulting from variations in manufacturing.