One way to improve the fuel efficiency of HVs is to reduce the losses and size of the Power Control Unit (PCU). To achieve this, it is important to reduce the losses of power devices (such as IGBTs and FWDs) used in the PCU since their losses account for about 20% of the total loss of an HV. Furthermore, another issue when reducing the size of power devices is ensuring the thermal feasibility of the downsized devices. To achieve the objectives of the 4th generation PCU, the following development targets were set for the IGBTs: reduce power losses by 19.8% and size by 30% compared to the 3rd generation. Power losses were reduced by the development of a new Super Body Layer (SBL) structure, which improved the trade-off relationship between switching and steady-state loss. This trade-off relationship was improved by optimizing the key SBL concentration parameter. Size was reduced by adopting a new environment-friendly IGBT surface electrode structural design that enabled double-sided solder packaging. This approach ensured thermal feasibility caused by the higher current density due to the smaller design. A REduced SURface Field (RESURF) structure was adopted for edge termination. To improve the robustness of the breakdown voltage, an optimum RESURF concentration balance was designed which also contributed to the IGBT’s downsizing. These developments successfully reduced both the loss and size of the IGBTs, thereby reducing the size and loss of the new PCU, and helping to improve the fuel efficiency of Toyota’s 4th generation HVs.