An efficient thermal management in electronic components is essential to minimize the influence of thermomechanically induced stress and thermal load. Frequently, thermal simulation tools are applied to reduce the number of experiments needed for thermal characterization of the semiconductor components. However, for using commercially available software packages, much effort is necessary for maintenance and for generating the thermal models. Moreover, the limitation of the node number does not allow a discretization sufficiently fine for more complex structures as in high lead count packages. In this paper, a new thermal simulation tool is presented, which allows one to create models in a very efficient way. The developed and implemented solver based on the alternating direction implicit method is efficiently processing the required high node number. Moreover, the developed thermal simulation tool is applied for the thermal characterization of a 176 lead quad flat pack (QFP-package) using a discretization with 320,000 nodes. Steady-state and transient thermal qualities of the package are investigated under boundary conditions as specified by the Joint Electronic Device Engineering Council (JEDEC). Further, results obtained by thermal simulation are compared with those established from experimental procedures. Conclusions of how this new tool can be used for thermal design optimization are derived.