ThSim provides simulation of temperatures in solid material. It uses SPICE to do the actual calculations. An electrical equivalent model is used in order to describe the thermal properties of the entered blocks of solid material. The simulation is limited to conduction; no flow or convection is included. The main usage of this software is to simulate short duration thermal effects of high power dissipation, for instance for semiconductor devices. It allows analyses for short time durations, where measurements are not possible. This tool provides a simple solution for thermal analyses in applications where the additional capabilities of high-end tools for simulation of thermal convection and flow are not necessary. The program uses wxWindows for the GUI and OpenGL for the 3D graphics output.