Semiconductor integrated circuit device

Efficient reduction in power consumption is achieved by combinational implementation of a power cutoff circuit technique using power supply switch control and a DVFS technique for low power consumption. A power supply switch section fed with power supply voltage, a circuit block in which a power cutoff is performed by the power supply switch section, and a level shifter are formed in a DEEP-NWELL region formed over a semiconductor substrate. Another power supply switch section fed with another power supply voltage, a circuit block in which a power cutoff is performed by the power supply switch section, and a level shifter are formed in another DEEP-NWELL region formed over the semiconductor substrate. In this arrangement, there arises no possibility of short-circuiting between different power supplies via each DEEP-NWELL region formed over the semiconductor substrate.