An X-ray detection device includes a gate electrode and a lower electrode on a substrate and laterally spaced from each other, a dielectric layer covering the gate electrode and the lower electrode, and a conductive pattern on the dielectric layer at a side of the gate electrode adjacent to the lower electrode and overlapping the lower electrode. The device also includes a source electrode spaced apart from the conductive pattern that is on the dielectric layer at the other side of the gate electrode, and an interlayer insulation layer covering the conductive pattern and the source electrode. A collector electrode, a photoelectric conversion layer, and a bias electrode are sequentially stacked on the interlayer insulation layer.