Memory devices and methods of forming the same are provided. A memory device includes a substrate, a first conductive layer, a phase change layer, a selector layer and a second conductive layer. The first conductive layer is disposed over the substrate. The phase change layer is disposed over the first conductive layer. The selector layer is disposed between the phase change layer and the first conductive layer. The second conductive layer is disposed over the phase change layer. In some embodiments, at least one of the phase change layer and the selector layer has a narrow-middle profile.