A memory device includes a substrate; a stack including a plurality of conductive layers and a plurality of insulating layers being alternatively stacked on the substrate; a plurality of memory structures formed on the substrate and penetrating the stack; a plurality of isolation structures formed on the substrate and penetrating the stack, wherein the isolation structures dividing the memory structures into a plurality of first memory structures and a plurality of second memory structures; and a plurality of common source pillars formed on the substrate and penetrating the stack, wherein the common source pillars directly contact the isolation structures.