A semiconductor integrated circuit device includes a semiconductor substrate and a ROM region, an SRAM region and a peripheral circuit region which are formed on the semiconductor substrate. Further, a column switch region is provided adjacent to the ROM region. MOS transistors in the ROM region and channel regions of access transistors in the SRAM region have substantially the same p-type impurity concentration. Accordingly, the threshold voltages of the transistors are adjusted by making use of the great dependence of the threshold voltage of the transistor on the channel width.