A semiconductor integrated circuit includes a power supply circuit having a global source line VCC, a local source line QVCC coupled to VCC by a source switching transistor, and a global ground line VSS, a low-threshold logic (combinational) circuit connected between QVCC and VSS, and a data storage (sequential) circuit, connected between VCC and VSS. The data storage circuit includes a low-threshold input section for receiving data from the logic circuit and a high-threshold latch section for latching the data received by the input section. Mode switching transistors are inserted between the low-threshold logic circuit and VSS, between low-threshold input section and VCC and between the low-threshold input section and VSS, for effecting a sleep mode of the semiconductor integrated circuit. Low power dissipation is maintained with a reduced circuit scale.