A thin-film transistor substrate and a display device comprising the same are provided which can improve display quality by reducing or preventing deterioration of the characteristics of thin-film transistors. The thin-film transistor substrate comprises thin-film transistors on a lower protective metal layer. Each thin-film transistor comprises a buffer layer, a semiconductor layer, a first insulating film, a gate electrode, a second insulating film, a source electrode and a drain electrode, and a first electrode. The lower protective metal layer is electrically connected to the gate electrode and overlaps the channel region of the semiconductor layer.