A thermoelectric energy harvesting system is proposed to supplement the primary power supply of an implantable medical device. A low-power synchronous boost converter capable of boosting 10mV input voltage to 1V output voltage is designed in a 180nm CMOS process. To increase the charging speed, a maximum power transfer scheme is utilized. The harvester delivers up to 10µW power with a minimum temperature gradient of 1-degree, which results in a power efficiency over 40%.Clinical Relevance- The use of this technology could enhance the longevity of battery-operated implanted medical devices by reducing the possibility of invasive battery replacement surgery.