A semiconductor storage device includes a memory cell array including a plurality of memory strings, each connected between one of a plurality of bit lines and a source line and includes a first select transistor, a second select transistor, and memory cell transistors that are connected in series between the first select transistor and the second select transistor, and a plurality of word lines respectively connected to gates of the memory cell transistors in each memory string. A threshold voltage of the memory cell transistor is increased when a voltage that is applied to the word line connected to the gate thereof is lower than a voltage of a channel thereof. In the erase operation, data stored in the memory cell transistors connected to a selected one of the word lines are erased while data stored in the memory cell transistors not connected to the selected word line are not erased.