A semiconductor storage device comprises a semiconductor layer; a plurality of memory cells formed on the semiconductor layer, data writing, erasing or reading with respect to each of the memory cells being possible based on a voltage applied to a control electrode and a voltage applied to the semiconductor layer; a first booster circuit supplying a voltage to control electrodes of selected memory cells into which data is to be written; and a second booster circuit supplying a voltage to control electrodes of inhibited memory cells into which data is not to be written, wherein when erasing data in the memory cells, a potential at the semiconductor layer is boosted in a first boosting mode in which a boosting capability of the first booster circuit is low and a boosting capability of the second booster circuit is high, and then the potential at the semiconductor layer is boosted in a second boosting mode in which the boosting capability of the second booster circuit is low and the boosting capability of the first booster circuit is high.