A display device includes a substrate, an active layer, a gate insulation layer, a gate electrode, an interlayer insulation layer, a clad layer, a source electrode, and a drain electrode. The active layer is disposed on the substrate. The gate insulation layer is disposed on the active layer. The gate electrode is disposed on the gate insulation layer. The interlayer insulation layer is disposed on the gate electrode. A dielectric constant of the interlayer insulation layer is less than a dielectric constant of the gate insulation layer. The clad layer is disposed on the interlayer insulation layer. The source and drain electrodes are disposed on the clad layer.