The objective of this research program is to study the underlying principles of carrier transport phenomena in semiconductor devices with ultrasmall spatial and/or temporal scales through the development of new and advanced numerical techniques. The general areas of research to be investigated are: 1) The development of a three- dimensional Monte Carlo device simulator. 2) The development of an algorithm for materials and device simulation which is based on the concept of occupation probability flux and the transition rate matrix. The new and advanced methods are expected t be more powerful, detailed and complete than conventional simulators, and can provide important techniques and tools to study some of the fundamental questions in carrier transport, such as anisotropy effects, non-stationary transport and quantum mechanical phenomena. Once the formulations are complete, each method will be applied to analyze various transport problems in materials and device structures through which the advantages of each method can be fully utilized and demonstrated. The knowledge developed in this work will be of crucial importance to the design optimization and feasibility study of novel electronic and optoelectronic devices, whose ever-decreasing dimensions render conventional simulation techniques more problematic and of declining value.