This paper presents an ultra-high power density point-of-load (PoL) converter based on a six-phase strongly coupled transformer (SCT) with least leakage inductance that can achieve unregulated voltage step-down for the second stage of Voltage Regulator Module (VRM). The least leakage inductance and high switching frequency ensure excellent transient performance of the converter. The structural design of smallest size and ultra-high power density for vertical power delivery makes it possible to place the converter closest to the microprocessor and minimize the impact of parasitic parameters on the efficiency of the PoL converter as well as on the transient performance. Firstly, this paper shows the structure of six-phase SCT. Secondly, the magnetic circuit model of the six-phase SCT is analyzed and verified by Maxwell 3D FEA. Finally, a prototype 6 V–1 V, 1 MHz, 90 A PoL converter was designed for experimental validation.