—This work presents a System-on-Chip designed for Energy-Harvested applications. It embeds an ARM Cortex-M0+ microcontroller, 4 KB RAM, 4 KB ROM, an ultra-low power frequency synthesizer, a custom power switch, and a Power Management Unit enabling Active and Sleep modes. The system fabricated in 28 nm FD-SOI technology achieves 2.7 pJ/cycle at 16 MHz during active mode, and the core consumes 4.3 nW during deep sleep mode. The system operates at a fixed voltage of 0.5 V, and can switch from Active and Sleep/Deep Sleep modes, adjusting the frequency from 16 MHz to 8 MHz or 32 kHz in one cycle upon energy availability. By combining frequency/power switching with extra Reverse Body-Biasing the system power consumption is reduced by 53% and 98% in respectively sleep and deep sleep modes.