A semiconductor memory device having a memory array comprising CMOS
flip-flop circuit type memory cells, which is capable of improving a noise
margin, making a read rate fast and reducing power consumption. In the
semiconductor memory device, an operating voltage of the memory cell is
set higher than an operating voltage of each of peripheral circuits.
Threshold voltages of MOS transistors that constitute the memory cell, are
set higher than those of MOS transistors constituting the peripheral
circuit. A gate insulting film for the MOS transistors that constitute the
memory cell, is formed so as to be regarded as thicker than a gate
insulting film for the MOS transistors constituting the peripheral circuit
when converted to an insulating film of the same material. Further, a
word-line selection level and a bit-line precharge level are set identical
to the level of the operating voltage of the peripheral circuit.
