The semiconductor industry faces two types of complexity. One is associated with generating and managing large amounts of data that define physical layouts. The other is associated with the nonlinear behaviors of semiconductor processes, devices, and circuits. Computer-aided design (CAD) tools help engineers deal with both types of complexity. Electronic design automation (EDA) software handles a range of tasks associated with the generation, verification, and storage of layout data. Physics-based process, device, and circuit simulators predict the behaviors that result from nonlinear phenomena. The apparently natural division of semiconductor CAD software into EDA tools and physics-based simulators of nonlinear phenomena is modified in practice by the fact that EDA tools and circuit simulators are used primarily by circuit designers, and process and device simulators are used primarily by technology developers. The CAD tools used by circuit designers are referred to as “electronics CAD (ECAD),” and the tools used by technology developers are referred to as “technology CAD (TCAD).” This partitioning of physics-based simulators by user communities can cause potentially useful connections between TCAD and circuit simulators to be neglected. These connections are the subject of this article.