Hybrid Super Threshold (SupVt) circuits are CMOS circuits that can function in two different operation modes: a normal operation mode and a SupVt power saving mode. At normal operation mode, a hybrid SupVt circuit operates in the same ways as typical CMOS circuits. At SupVt mode, the standby leakage current of the circuit is reduced significantly, while the circuit still can function at high speed. Typically, most parts of a hybrid SupVt 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.