This article presents a fully integrated, high conversion ratio, three-level switched-capacitor (SC) power converter. The converter adopts a tri-mode operation in contrast to classic dual-mode operation in conventional SC converters. The unique circuit structure and operation create an inherent third power rail, which facilitates the use of low-voltage devices at high supply voltage for fast speed and low-silicon real estate. The tri-mode operation naturally matches a three-phase interleaving scheme for improved output voltage ripple and transient response. Implemented on a 0.35-μm BCD process, the design prototype accomplishes a conversion ratio greater than 4:1 and a maximum power delivery of 180 mW at 6-V input and a switching frequency of 93 MHz. With the efficient use of on-chip power switches and capacitors, it achieves a maximum power density of 125 mW/mm<sup>2</sup>.