Needs for low-power CMOS devices are still increasing. Ultralow-voltage-operation CMOS with maximum power efficiency can extend the application field of electron devices: ubiquitous sensor network, etc. The main issues for low-power (high-efficiency) operation for the modern scaled CMOS are reducing variability and adaptive control of circuit performances enabling the operation at voltages as low as possible. In order to solve these issues, we are developing the silicon-on-thin-buried-oxide (SOTB) transistors. Features of the SOTB, transistor technology dedicated for ultralow-voltage operation are presented and importance of device-circuit interaction to extend the application field is discussed.