Thermal effects may represent a limiting factor in the development of integrated circuits. As the power dissipated by integrated circuits becomes more relevant, the need increases for more accurate modelling of the stationary and transient thermal behaviour of the die-package structure. In this paper, an analytical solution of the three-dimen-sional transient thermal diffusion problem is presented, together with a simple computer program for the calculation of the solution. The program, implemented on a minicomputer, is proven to be fast and accurate. The simulation technique is then applied to the design of a new short-circuit protection of a 6A current booster.