A thin film transistor (TFT) substrate comprises a TFT located on a substrate and including a gate electrode, a first semiconductor layer and a second semiconductor layer, wherein the first semiconductor layer, the gate electrode and the second semiconductor layer vertically stacked, and the first and second semiconductor layers are made of polycrystalline silicon, and wherein the first and second semiconductor layers are electrically connected to each other in series and respectively include first and second channel portions, and at least one of the first and second channel portions has a bent structure in a plan view.