One of the major difficulties in analyzing real-life engineering systems is the interaction amongst many different physical phenomena and their closely interconnected couplings. The purpose of this work is to develop a coanalyses methodology to address both electromagnetic (EM) and thermal effects for modeling high power integrated circuit (ICs), package and printed circuit boards (PCB). We use non-conformal domain decomposition method (DDM) for both electric and thermal analysis of high-power ICs. Non-conformal DDM decomposes the original problem domain into several non-overlapping sub-domains and thus can be effective for solving multiscale engineering problems. Furthermore, in the current approach, the thermal cooling is performed through heat sinks with both natural convection and air forced convection cooling.