This book summarizes the research of more than a decade. Its early motivation dates back to the eighties and to the memorable talks Dr. C. Moglestue (FHG Freiburg) gave on his Monte-Carlo solutions of the Boltzmann transport equation at the NASECODE conferences in Ireland. At that time numerical semiconductor device modeling basically implied the application of the drift-diffusion model. On the one hand, those talks clearly showed the potential of the Monte-Carlo model for an accurate description of many important transport issues that cannot adequately be addressed by the drift-diffusion...