Hybrid circuits are CMOS circuits that can function in two different operation modes: a normal operation mode and a power saving mode. At normal operation mode, a hybrid circuit operates in the same ways as typical CMOS circuits. At power saving mode, the standby leakage current of the circuit is reduced significantly. Typically, most parts of a hybrid circuit stay in power saving mode. A circuit block is switched into normal operation mode when it needs to operate at full speed. The resulting circuits are capable of supporting ultra-low power operations without sacrificing performance. Hybrid circuits can be implemented on integrated circuits comprising multiple-gate MOS transistors.