This paper presents a 1 mm² solar cell and a Power Management Unit (PMU) on the same substrate to rise up the harvested voltage above 1.1 V to power wearable or implantable devices. The on-chip solar cell and the PMU are fabricated in standard 0.18 μm CMOS technology achieving a form factor of 1.575 mm². Experimental results show that the PMU is able to start-up from a harvested power of 2.38 nW without any external kick off or control signal and can handle a harvested power up to μW with a continuous and two-dimensional Maximum Power Point Tracking (MPPT) that works in open-loop mode to set the frequency, the gain and the capacitor sizes of a charge pump.