A memory array, a semiconductor chip and a method for forming the memory array are provided. The memory array includes first signal lines, second signal lines and memory cells. The first signal lines extend along a first direction. The second signal lines extend along a second direction over the first signal lines. The memory cells are defined at intersections of the first and second signal lines, and respectively include a resistance variable layer, a switching layer, an electrode layer and a carbon containing dielectric layer. The switching layer is overlapped with the resistance variable layer. The electrode layer lies between the resistance variable layer and the switching layer. The carbon containing layer laterally surrounds a stacking structure including the resistance variable layer, the switching layer and the electrode layer.