In this paper, a high power-density 3D integrated synchronous buck converter with dual side cooling structure was designed and analyzed. A novel panel-level PCB embedded package technology for MOSFETs and planar LTCC inductor of the converter was proposed to address parasitic elements, heat dissipation, and reliability issues inherent with aluminum wires used in conventional wire-bonded package. The MOSFETs and LTCC inductor were embedded in the PCB, respectively, interconnected by RDL and PCB vias. Copper-clad BT laminate and BT prepreg with low CTE and high Tg were selected and characterized by TMA. Analysis showed that the selective PCB embedding materials were very ideal for MOSFETs and LTCC inductor packaging. Thermal simulation of the 3D module was performed using ANSYS ICEPAK. To improve accuracy and efficiency of the thermal simulation, equivalent thermal conductivity of a PCB via unit was extracted and equivalent model was built. Effects of PCB vias and heat spreader on the thermal performance of the 3D converter were analyzed. The study showed that PCB vias can improve the thermal performance of the 3D module with cap heat spreader. The highest junction temperature of the optimized 3D converter was limited to about 71.2 °C.