For the printed circuit boards for the power electronics, whether the simulation of the temperatures of parts was possible by the commercial CFD analysis was compared with the experiment and I examined it. Moreover, the influence of the heat sink thickness was examined. As a result, If you set the thermal conductivity of the boards and the heaters to an appropriate mean value by CFD analysis, an experiment value and an analytical value were able to be brought close. When the heat sink was not installed, it was about ± 5.0℃. On the other hand, when the heat sink was installed, it was about ± 7.0℃. In addition, it was predictable that the effect of the heat sink was not ruined even if the thickness of the heat sink was thinned.