A thin film transistor includes a layer structure having a gate electrode, a gate insulation layer and a channel layer. A source line may contact the channel layer, and may extend along a direction crossing over the gate electrode. The source line may partially overlap the gate electrode so that both sides of the source line overlapping the gate electrode may be entirely positioned between both sides of the gate electrode. A drain line may make contact with the channel layer and may be spaced apart from the source line by a channel length. The drain line may have a structure symmetrical to that of the source line. Overlap areas among the gate electrode, the source line and the drain line may be reduced, so that the thin film transistor may ensure a high cut-off frequency.