We have developed a method for deriving a set of supply voltage and threshold voltage that enables the circuit to operate at the minimum energy consumption under a wide range of operating conditions and a specified delay constraint. We experimentally confirmed using a fabricated 32-bit processor that the derived set of supply voltage and threshold voltage can operate the circuit with less than 5 % excess energy from the minimum energy consumption under a wide variety of delay constraints and operating conditions. We also developed a DLL-type body bias generator that generate P/N well-voltages independently so that the energy consumption becomes minimum, which was verified by fabricated test chips.