A layered film of a three-layer clad foil formed with a first metal layer 23, a second metal layer 25, and an inorganic insulating layer 35 interposed therebetween is prepared. After the second metal layer 25 is partially etched to form a gate electrode 20g, the first metal layer 23 is partially etched to form source/drain electrodes 20s, 20d in a region corresponding to the gate electrode 20g. A semiconductor layer 40 is then formed in contact with the source/drain electrodes 20s, 20d and on the gate electrode 20g with the inorganic insulating layer 35 interposed therebetween. The inorganic insulating layer 35 on the gate electrode 20g functions as a gate insulating film 30, and the semiconductor layer 40 between the source/drain electrodes 20s, 20d on the inorganic insulating layer 35 functions as a channel.