A semiconductor memory device includes a memory block, a peripheral circuit, and control logic. The memory block includes a plurality of string groups respectively connected to a corresponding source select line among a plurality of source select lines. The peripheral circuit is configured to perform a program operation of storing data within the memory block. The control logic controls the program operation of the peripheral circuit. The plurality of source select lines are grouped into a plurality of source select line groups. The control logic controls the peripheral circuit to increase a voltage of a first source select line group including a source select line connected to a selected string group to a first level among the plurality of source select line groups.