A thin film transistor comprises a source over a substrate; a first insulation layer having a source contact through-hole corresponding to a position of the source over the source; an active layer electrically connecting with the source through the source contact through-hole over the etching stop layer; a second insulation layer having a drain contact through-hole exposing a portion of the active layer over the active layer; and a drain electrically connecting with the active layer through the drain contact through-hole over the second insulation layer.