To speed up operation of a sense amplifier through amplification of signal read from a memory cell by boosting up a threshold voltage using a voltage setting circuit to control a substrate voltage of a transistor forming the sense amplifier.

A sense amplifier S/A is activated by the signals SAP and /SAN under the condition that the potential of substrate terminals of four transistors Qn1, Qn1, Qp1, Qp2 is 0.5 × VCC. In this case, the sense amplifier S/A senses and amplifies only a light change of voltage of the bit line explained above and also amplifies the potentials of the bit line pair BL and/BL respectively to H and L levels. As explained above, data is read from the memory cell.