Power supply impedance of power distribution network (PDN) for a 3D system-in-package (SiP) has been investigated. The 3D SiP consisted of 3 stacked chips and an organic package substrate. These three chips were a memory chip on the top, Si interposer in the middle, and a logic chip on the bottom. The size of each chip was the same, and 9.93 mm by 9.93 mm. A large number of through silicon vias (TSV's) were formed to the silicon interposer and the logic chip. Next, the 3 stacked chips were assembled on the organic package substrate, whose size was 26 mm by 26 mm. The PDN impedance for each chip was extracted by using XcitePI (Sigrity Inc.). Then, the PDN impedance for the organic package substrate was extracted by using SIwave (Ansys Inc.). Finally, the total PDN impedance was synthesized. In this paper, the PDN impedances of the memory chip, Si interposer, and the logic chip were calculated respectively, and then the total PDN impedance was synthesized to estimate the power supply disturbance due to the anti-resonance peak.