A memory device includes a first electrode, a resistive switching layer, a cap layer, a protective layer, and a second electrode. The resistive switching layer is disposed over the first electrode. The cap layer is disposed over the resistive switching layer, wherein the bottom surface of the cap layer is smaller than the top surface of the resistive switching layer. The protective layer is disposed over the resistive switching layer and surrounds the cap layer. At least a portion of the second electrode is disposed over the cap layer and covers the protective layer.