A
semiconductor integrated circuit wherein the circuit area can be minimized, and defects can be detected reliably during a standby status while maintaining the reliability of a
gate oxide film. Switching circuit 20 is provided between logic circuit 10 and source
voltage Vdd supply terminal. While in an operating status, 0 V
voltage is applied to the gate of
transistor MP0 of switching circuit 20, and bias
voltage VB equal to or slightly lower than source voltage Vdd is applied to its channel region in order to reduce the
threshold voltage of
transistor MP0 and increase its current driving capability. While in a standby status, a voltage equal to source voltage Vdd is applied to the gate of
transistor MP0, a voltage lower than the source voltage is applied to the source, and bulk bias voltage VB equal to or higher than source voltage Vdd is applied to the channel region in order to minimize the
drain current of transistor MP0, so that current path of logic circuit 10 is
cut off, and the occurrence of leakage current is suppressed.