Disclosed are memory devices including a two-dimensional (2D) material, methods of manufacturing the same, and methods of operating the same. A memory device may include a transistor, which includes graphene and 2D semiconductor contacting the graphene, and a capacitor connected to the transistor. The memory device may include a first electrode, a first insulation layer, a second electrode, a semiconductor layer, a third electrode, a second insulation layer, and a fourth electrode which are sequentially arranged. The second electrode may include the graphene, and the semiconductor layer may include the 2D semiconductor. Alternatively, the memory device may include first and second electrode elements, a graphene layer between the first and second electrode elements, a 2D semiconductor layer between the graphene layer and the first electrode element, and a dielectric layer between the graphene layer and the second electrode.