This paper presents a highly efficient 3-stage boost converter with an isolated Power-on-Reset (PoR) based starter for thermal energy harvesting. The automatic pulse generation property of the proposed PoR is coupled with a charge-pump (CP) based clock enhancer (CE) to enhance the gate-driving capability for fast and efficient boost conversion during startup. Unlike conventional PoR-based startup circuits, where the reset signals cannot be directly utilized to execute a boost conversion during startup, the proposed starter converts a chain of pulses from the PoR into level-shifted clock signals to aid direct boost conversion from sub-threshold voltages. The proposed boost converter has a minimum self-startup TEG voltage of 150 mV at the series resistance (ESR) of 450 Ω without using external devices or native MOSFET. The maximum ESR for startup is 600 Ω at the TEG voltage of 320 mV. The peak power conversion efficiency of the proposed boost converter is 78 %.