Disclosed is a semiconductor device in which substantial enhancement of a write margin without degradation of a static noise can be achieved while obviating an increase in physical circuit size. There are disposed a plurality of power supply lines for feeding a power supply voltage to each column of static memory cells that use complementary bit lines in common; a plurality of power switches, each being disposed for each of the power supply lines; and a plurality of short-circuit switches, each being so arranged as to provide short-circuiting between output nodes of different power switches. When a complementary bit line select signal indicates an unselected level, the power switch corresponding thereto is put in an ON state so that, in a read operation, a power supply voltage is fed via the short-circuit switch concerned to a selected memory cell column from the power supply line corresponding to a memory cell being unselected, or in a write operation, a power supply voltage fed via the short-circuit switch concerned to a selected memory cell column is stopped.