A leakage current monitor circuit was developed for dynamic back gate bias control of CMOS LSI with Silicon on Thin BOX (SOTB) technology. By using the SOTB technology, sensors or wearable devices can suppress the leakage power by giving deep reverse body bias when they are not used. Once an event occurs, they must turn to the operational mode by changing the body bias quickly. According to the real chip evaluation, it takes hundreds of micro seconds, and the wake-up time is difficult to be estimated. The proposed detector using a leakage current monitor circuit guarantees that the target module is ready to be operational. The target body bias voltage for operation can be controlled by the bias voltage of the detector domain, which is computed with an expression in advance. SPICE simulation reveals that formulation is done and power overhead is only 42.7-42.9nW in the room temperature. Compensation equations for various temperatures are also shown.