A display panel comprising: a base substrate; a thin-film transistor disposed on a surface of the base substrate, the thin-film transistor including a gate electrode, a semiconductor layer overlapping the gate electrode, and a source electrode and a drain electrode disposed over the semiconductor layer; a first insulating layer disposed over both the source electrode and the drain electrode; and a data line and a connection electrode disposed over the first insulating layer, wherein the first insulating layer is disposed between the gate electrode and each of the data line and the connection electrode, wherein the data line is electrically connected to the source electrode via a first contact hole penetrating through the first insulating layer, wherein the connection electrode is arranged to extend through a second contact hole penetrating through the first insulating layer to electrically connect the drain electrode to a pixel electrode of the display panel, and wherein the source electrode is configured to supply a data voltage from the data line to the semiconductor layer, and the connection electrode is configured to supply the data voltage from the drain electrode to the pixel electrode, wherein a thickness of a cross section of each of the source electrode and the drain electrode is less than or equal to half a thickness of a cross section of each of the data line and the connection electrode, wherein the thickness of the cross section of each of the source electrode and the drain electrode is 50 nm to 200 nm, wherein the thickness of the cross section of each of the data line and the connection electrode is 500 nm to 2000 nm, wherein the source electrode includes a portion which directly contacts the semiconductor layer, wherein the data line includes a portion which extends through the first contact hole penetrating through the first insulating layer to directly contact the source electrode, and wherein the portion of the data line and the portion of the source electrode overlap each other in a direction perpendicular to the surface of the base substrate. a base substrate; a thin-film transistor disposed on a surface of the base substrate, the thin-film transistor including a gate electrode, a semiconductor layer overlapping the gate electrode, and a source electrode and a drain electrode disposed over the semiconductor layer; a first insulating layer disposed over both the source electrode and the drain electrode; and a data line and a connection electrode disposed over the first insulating layer, wherein the first insulating layer is disposed between the gate electrode and each of the data line and the connection electrode, wherein the data line is electrically connected to the source electrode via a first contact hole penetrating through the first insulating layer, wherein the connection electrode is arranged to extend through a second contact hole penetrating through the first insulating layer to electrically connect the drain electrode to a pixel electrode of the display panel, and wherein the source electrode is configured to supply a data voltage from the data line to the semiconductor layer, and the connection electrode is configured to supply the data voltage from the drain electrode to the pixel electrode, wherein a thickness of a cross section of each of the source electrode and the drain electrode is less than or equal to half a thickness of a cross section of each of the data line and the connection electrode, wherein the thickness of the cross section of each of the source electrode and the drain electrode is 50 nm to 200 nm, wherein the thickness of the cross section of each of the data line and the connection electrode is 500 nm to 2000 nm, wherein the source electrode includes a portion which directly contacts the semiconductor layer, wherein the data line includes a portion which extends through the first contact hole penetrating through the first insulating layer to directly contact the source electrode, and wherein the portion of the data line and the portion of the source electrode overlap each other in a direction perpendicular to the surface of the base substrate.