A direct sense amplifier isolates an MOS transistor serving as a differential pair having a gate being connected with a bit line from an RLIO line by inserting an MOS transistor being controlled by a column select line arranged in the direction of the bit line between them and connects the source of the MOS transistor serving as a differential pair with a common source line arranged in the direction of the word line. Power consumption is reduced greatly at the time of read operation by activating the direct sense amplifier only at a select mat through the column select line and the common source line. Higher-rate reading operation is realized by isolating the parasitic capacitance of the MOS transistor serving as a differential pair from a local IO line thereby reducing the load capacity of the local IO line, and test after fabrication is facilitated by reducing the data pattern dependency of the load capacity of the local IO line during the reading operation.
