An accurate three-dimensional analysis of semiconductor devices based on the general transport equations is carried out. In this analysis, the finite difference formulation and ICCG (Incomplete Choleski and Conjugate Gradient) methods are utilized to reduce computational time and memory requirements. The algorithms are applied to a wide variety of devices, including a bipolar n-p-n transistor, an Integrated Injection Logic (ILL), and a Static Induction Transistor (SIT). Calculated results are compared to those obtained using a conventional two-dimensional simulator. Several three-dimensional effects are modeled successfully. These analyses make it clear that three-dimensional calculation is indispensable for accurate device modeling.