In recent years, there is a growing demand to have smaller and lighter electronic circuits which have greater complexity, multifunctionality and reliability. High-density multichip packaging technology has been used in order to meet these requirements. The higher the density scale is, the larger the power dissipation per unit area becomes. Therefore, in the designing process it has become very important to carry out the thermal analysis. However, the heat transport model in multichip modules is very complex and its treatment is tedious and time consuming. This paper describes an application of the thermal network method to the transient thermal analysis of multichip modules and proposes a simple model for the thermal analysis of multichip modules as a preliminary thermal design tool. Based on the result of transient thermal analysis, the validity of the thermal network method and the simple thermal analysis model are confirmed.