In recent years, thermal design has become more and more important as electronic devices become smaller and more powerful. There is a great interest in the application of structural optimization to the field of thermal design. In this study, topology optimization was performed to find a structure that minimizes the temperature of the heat supply section. As a result, we obtained a structure that is not useful for engineering purposes under some conditions. This was caused by the non-convexity of the problem, which is difficult to handle with this method, and it became clear that another solution method needs to be developed.