Each of memory strings is provided with a first semiconductor layer having a pair of columnar portions extending in a perpendicular direction with respect to a substrate; a charge storage layer formed to surround a side surface of the columnar portions; and a first conductive layer formed to surround the charge storage layer. Each of the select transistors is provided with a second semiconductor layer extending upwardly from an upper surface of the columnar portions; a gate insulating layer formed to surround a side surface of the second semiconductor layer; and a second conductive layer formed to surround the gate insulating layer. An effective impurity concentration of the second semiconductor layer is less than or equal to an effective impurity concentration of the first semiconductor layer.