This research proposes a third-generation power control unit(PCU) for a two-motor hybrid system. To make a more compact intelligent power unit(IPU) for being located under 2nd seat, a PCU with a 12-volt DC-DC converter that mounts directly on the transmission was developed, whereas the converter was previously mounted within the IPU. Since this has a considerable impact on the engine room layout, the technology described below was used to make the PCU even more compact than the second-generation unit. The power module, a key component of the PCU, now uses the Ag nanoparticles sintering bonding rather than the conventional solder bonding. This helps lower thermal resistance and enables a smaller power semiconductor. The voltage control unit(VCU) has a new system that uses a multi-stage switching circuit and electric power transfer capacitor instead of the conventional chopper system. This makes it possible to shrink the reactor to less than 65% of its usual volume without raising the carrier frequency, and enables a layout that efficiently uses both sides of the heat sink, so that no specially designed heat sink needs to be added just for the 12-volt DC-DC converter. As for the heat sink seal, friction stir welding(FSW) to increase rigidity was used to reduce seal width and to make the heat sink itself more compact. The use of these compactness technologies enabled the PCU to maintain all the efficiency of the second-generation PCU and made it possible to build the 12-volt DC-DC converter while maintaining the PCU’s volume. Development of this PCU makes the IPU much more compact and provides a similar amount of trunk space as in a gasoline-powered vehicle.