The present disclosure relates to a semiconductor device and a method of operating the semiconductor device, and particularly to a semiconductor memory device including a memory cell array and a method of operating the semiconductor memory device. The memory device includes a memory cell array including a plurality of memory cells; and a peripheral circuit configured to program a selected memory cell into a target program state, wherein the peripheral circuit performs a program operation by applying a bit line voltage determined according to the threshold voltage to a bit line of the selected memory cell when a threshold voltage of the selected memory cell is higher than a first verification voltage and is lower than a second verification voltage.