A thin film transistor includes a semiconductor formed on a substrate and having a source region, a first drain region spaced apart from the source region by a first current channel, and a second drain region spaced apart from the source region by a second current channel which has the different length from that of the first current channel, a gate electrode insulated from the semiconductor by a gate insulating layer, a source electrode connected to the source region of the semiconductor, a first drain electrode connected to the first drain region of the semiconductor, a second drain electrode connected to the second drain region of the semiconductor, and a bypass line electrically connecting the first drain region and the second drain region.