A thin film transistor substrate and a fabricating method thereof wherein a contacting size between an electrode and an active layer can be reduced to provide a small and light panel. Two three or four magnetrons supply microwave energy to the launch box, and hence into the oven cavity, via corresponding waveguides each in communication with a respective side of the launch box. One of the first and second transistors is constituted by a MOS field-effect transistor having a drain connected to the output terminal.