A high-voltage (15 kV) power transformer using multilayer printed circuit board (ML-PCB) technology is presented for applications in switched-mode power supplies, whose output power is 4.5 kW, and inverting frequency is 20 kHz. A new configuration for the magnetic core is proposed based on planar EI cores. The parallel connection of planar cores was adopted as a unit, and several units were cascaded to form the high voltage transformer. Manufacturing the PCB involves small tolerances, so the transformer exhibits parasitic effects which are highly reproducible from a production viewpoint. The mechanical configuration of a laboratory prototype is discussed, as well as the electrical, parasitic, and thermal behaviors. The transformer was tested and found to have an efficiency of better than 96%. Compared with traditional high voltage transformers, this transformer has good thermal behavior, good line insulation properties and a high power density.