In order to establish the basic technology of package level DC power grid for next generation power delivery to LSIs, Zn-ferrite core planar power inductor embedded in an organic interposer for power supply integrated in LSI package, has been fabricated and evaluated. Zn-ferrite core planar power inductor embedded in organic interposer had a footprint of 850×850 μm2, 2-turn, 20 μm thick copper spiral coil sandwiched by top and bottom Zn-ferrite film magnetic core. For a comparison, a 3-turn air core spiral inductor was also embedded in the same organic interposer, which exhibited a large degradation of inductance at high frequencies because of eddy current induced by widespread high frequency magnetic flux passing through the lower layer Cu metal plane. Zn-ferrite core planar inductor had a relative small decrease of inductance at high frequencies. From 3D electromagnetic field analysis, it was found that the magnetic core inductor embedded in interposer has a great advantage of a possible three dimensional layout of the inductor with small influence on the near signal-line and circuit ground.