The paper presents the design and measurements for very high frequency, low power, inductive DC-DC converters (100 MHz, 3:3 V input voltage, 350 mW output power). Preliminary analyses including the state-of-the-art, the architecture and the technology are briefly discussed. A converter is designed as a power system-in-package, based on a cascode power stage in a 2.5D assembly using a capacitive interposer embedding deep trench capacitors. Experimental characterizations are presented. An efficiency of 90 % is demonstrated while converting from 3:3 V to 2:4 V and supplying 150 mA, showing a + 8 % efficiency improvement compared to a converter with a standard power stage.