This paper presents a fully integrated step-up switched-capacitor DC-DC converter for energy harvesting applications. The proposed solution exhibits both a high voltage-conversion ratio and a high power-conversion efficiency from a low-voltage source such as a thermoelectric generator or an indoor solar cell. The circuit has been implemented in TSMC 55nm CMOS process. Measurements demonstrate that it can properly operate with a 220 mV input, providing a 1.9 V output voltage at 10.45 μW output power, with 37.4% power conversion efficiency. We demonstrate that it can be used as a power supply for a Bluetooth Low Energy beacon with a thermoelectric generator subjected to a temperature difference of only 3.5°C.