A DRAM whose operation is sped up and power consumption is reduced is provided. A pair of precharge MOSFETs for supplying a precharge voltage to a pair of input/output nodes of a CMOS sense amplifier is provided; the pair of input/output nodes are connected to a complementary bit-line pair via a selection switch MOSFET; a first equalize MOSFET is provided between the complementary bit-line pair for equalizing them; a memory cell is provided between one of the complementary bit-line pair and a word line intersecting with it; gate insulators of the selection switch MOSFETs and first equalize MOSFET are formed by first film thickness; a gate insulator of the precharge MOSFET is formed by second film thickness thinner than the first film thickness; a precharge signal corresponding to a power supply voltage is supplied to the precharge MOSFET; and an equalize signal and a selection signal corresponding to a boost voltage are supplied to the first equalize MOSFET and the selection switch MOSFET, respectively.