This paper presents a Colpitts oscillator-based self-starting boost converter for thermoelectric energy harvesting. An enhanced swing Colpitts oscillator with a 10-stage voltage multiplier is adopted as a startup circuit so that the minimum startup voltage of 40 mV is achieved. As a main converter, a zero-current-switching boost converter with a dead time controller achieves the maximum end-to-end efficiency of 75%. The inductor used in the Colpitts oscillator is reused in the main boost converter to minimize the use of the inductor. Implemented in a 65-nm CMOS, the proposed converter that requires only two external inductors provides a regulated output voltage of 1.1 V from a thermoelectric generator with an internal resistance of 2.2 Omega over the input range of 40-200 mV.