Power converters and semiconductor devices are spreading their application fields, due to new renewable energy and automotive frameworks. In the electrified vehicles context, the even more stringent requirements, both in terms of performances and reliability, pose new challenges in the design phase of power switches. This paper analyzes, by means of finite-element simulations, a low-voltage power semiconductor system-in-package devoted to automotive applications, which integrates a MOSFET-based half bridge and a controller. Three simulation physical domains integrated in a unique flow are considered: thermo-mechanical, electromagnetic, and thermal numerical models. The aim is to develop a new comprehensive methodology which starts with a thermo-structural simulation of the package, then computes the on-state resistance and parasitic components to assess the electrical behavior of the package. Finally, a simulation check is made to verify if the power device performances are thermally consistent with applicative conditions.