The present study is concerned with the determination of the optimal shape for packages containing heating substrates or objects. An design optimization tool has been developed based on an inverse heat transfer (IHT) approach, which incorporates a direct problem solver, a grid generator, a sensitivity analyzer, and the conjugate gradient method. Shape design that features an isothermal outer surface or meets other specified thermal requirements is predicted by the approach. In this study, the effects of internal heat generation on optimal shapes of the packagings have been evaluated. Several practical cases with various imbedded heating objects and thermal boundary conditions are studied to demonstrate the performance of the approach.