A semiconductor memory device includes a memory string and a control logic. The memory string is connected between a common source line and a bit line and includes at least one first select transistor, a plurality of memory cells, and a plurality of second select transistors. The control logic is configured to apply a first voltage to a first group among second select lines respectively connected to the second select transistors, float a second group among the second select lines and then apply an erase voltage to the common source line, during an erase operation.