This paper proposes a cold-startup circuit for 0.5-V open-circuit voltage (V_{OC}). The 4 series-connected sub-PTs are used to generate a 4X V_{OC} to build up V_{DD} and change to parallel to extract more power. A LDO is used to generate 1.8-V V_{DD}. A charge-up block is used to help V_{PT} overcome the threshold voltage after cold-startup. A SSHI rectifier is used to improve the output power efficiency by flipping V_{PT}. Corresponding simulation results show that 1.8-V V_{DD} can be built up even with 0.5-V V_{OC}. The simulated maximum output power is 24X larger than the output power of the FBR.