Method of programming a select transistor of a semiconductor memory device

Abstract

A semiconductor memory device includes a first cell string, a second cell string, a peripheral circuit, and a control logic. The first cell string includes first and second drain select transistors. The second cell string includes third and fourth drain select transistors. The peripheral circuit performs a program operation on the fourth drain select transistor included in the second cell string. The threshold voltage of the first drain select transistor is set through an ion implantation process. The threshold voltage of the fourth drain select transistor is set through the program operation.