Energy-efficiency has become the driving force of today's LSI industry. In order to achieve minimum energy operation of LSI, we propose a built-in body biasing technique which generates independent body biases for nMOSFET and pMOSFET separately. We design and fabricate an application circuit integrated with our proposed built-in body bias generation (BBG) circuits in a 65-nm process. The application circuit consists of AES cipher and decipher modules. The BBG does not require an external supply and it is compatible with a dynamic voltage scaling scheme for the application circuit. Cell-based design of the BBG circuit has been applied to facilitate automatic place and route. Both of the AES and the BBG circuits have been routed simultaneously to reduce design and area overhead. In post-silicon, supply voltage and body bias voltages are selected to achieve the minimum energy consumption for a target frequency. From the measurement results, more than 20% of energy reduction is achieved compared with adjusting supply voltage alone.