A thin film transistor substrate according to an embodiment comprises: a support substrate; a bonding layer disposed on the support substrate; a thin film transistor disposed on the bonding layer, wherein the thin film transistor includes a channel layer containing a nitride-based semiconductor layer, a source electrode electrically connected to a first region of the channel layer, a drain electrode electrically connected to a second region of the channel layer, a gate electrode disposed below the channel layer, and a depletion forming layer disposed between the channel layer and the gate electrode; and a pixel electrode disposed on the thin film transistor and electrically connected to the drain electrode of the thin film transistor. The thin film transistor substrate according to the embodiment, and a display panel and a display device including the same have an advantage of implementing high resolution and reproducing a soft moving image by providing a high carrier mobility.