In a thin-film transistor (TFT) substrate, a gate insulating layer is disposed on a gate electrode electrically connected to a gate line. A semiconductor layer is disposed on the gate insulating layer. A source electrode is electrically connected to a data line that intersects the gate line. A drain electrode faces the source electrode and defines a channel area of a semiconductor layer. An organic layer is disposed on the data line and has a first opening exposing the channel area. An inorganic insulating layer is disposed on the organic layer. A pixel electrode is disposed on the inorganic insulating layer and electrically connected to the drain electrode. The inorganic insulating layer covers the first opening, and thickness of the inorganic insulating layer is substantially uniform.