The invention discloses a display device which comprises a substrate, a thin film transistor on the substrate, and a display element which is on the substrate and is electrically connected with the thin film transistor. The thin film transistor includes an active layer over a substrate, a gate electrode over the active layer, a gate line connected with the gate electrode, and a gate insulation film between the active layer and the gate electrode. The active layer includes a channel region overlapping the gate electrode, and a drain region and a source region on respective sides of the channelregion. A length of a straight line connecting the drain region and the source region by a shortest distance may be greater than a width of the gate line parallel to the straight line.