This paper presents the design, fabrication, and characterization of micro planar inductors on a microwave magnetic material (YIG). Planar spiral inductors were designed for monolithic DC-DC converters in System-In-Package with 100 MHz switching frequency (1 W, Vin=3.6 V, Vout=1 V). System-In-Package applications are facing miniaturization issues due to passive components size. In this frequency range, the size of filter passive components can be reduced dramatically. Thus, the passive area of integration is in the 10 mm2 range. A microwave magnetic substrate (YIG) serves as mechanical support and also presents a double purpose by increasing inductance value and reducing electromagnetic perturbations. This last point seems to be a critical point to improve the good behavior of a switching mode power supply. In order to obtain the optimal design for the inductor, geometrical parameters were studied using Flux2D simulator. A specific Merit factor taking into consideration inductance value at 100MHz, DC resistance and footprint was proposed to compare different inductor structures. An optimized 50 nH spiral inductor with expected 50 mΩ RDC, 3 mm2 surface area was designed. Simulation conditions and results will be described in the full paper. Micro inductors occupying 3mm2 surface area were fabricated by electroplating technique. Fabrication process involves seed layer deposition on YIG, lamination of dry film photoresist and electroplating to mould the resist patterns. Process fabrication will be detailed in the full paper. Figure 1 shows SEM image of the fabricated inductor. Afterwards, samples were tested using a vector network analyzer in the 10 MHz to 100 MHz range. Results were then compared to the predicted response of simulated equivalent model.