In power electronics, especially in the area of sustainable mobility through electric vehicles (EVs), the aim is to have power-efficient and compact power electronic systems. Electric vehicles commonly use traction inverters which are generally highly complex systems with a large number of parameters. In the context of Multi-Objective Optimization (MOO) it is indispensable to have surrogate models which are cheap to evaluate, because sufficiently many Spice or 3D system level simulation are most likely not feasible. The aim of this work is to demonstrate the capabilities of Surrogate-Based Optimization for complex traction inverter systems having a large number of design parameters.