This article proposes a novel four-phase series-parallel resonant switched-capacitor (ReSC) 16:1 DC-DC converter topology with 16 GaN switches, 5 flying capacitors, and 1 inductor under soft-switching conditions. The topology provides a large conversion ratio and can serve as the first stage in a two-stage 48-V step-down voltage-regulated module (VRM) for data centers and is expected to generate a 3V intermediate voltage, reducing voltage stress on the second stage. A discrete prototype was made to validate the topology and achieves 96.5% peak efficiency and up to 460 W/in³ power density.