An UHF RF energy harvester with integrated stepup converter is presented. This system is designed to overcome the limits of standard RF harvesters (namely low output voltage). This objective is obtained with an extra DC/DC converter that provides an extra voltage boost, with less than 10 nW of power consumption. The accurate sub-threshold analysis of this converter allowed a start-up voltage as low as 200 mV, without compromising the overall power efficiency. The final system is intended to provide an output voltage high enough to power standard common loads (ex. microcontroller) and, more in general, any IoT wireless sensor node, with a limited amount of received power. This is confirmed by experimental results: an output voltage above 1.2 V is obtained starting from a received power of about -24 dBm. The step-up converter area is only 230 mu m x 375 mu m.