This paper discusses a methodology for quickly investigating problem areas in semiconductor wafer fabrication factories by creating a model for the production area of interest only (as opposed to a model of the complete factory operation). All other factory operations are treated as "black boxes". Specific assumptions are made to capture the effect of reentrant flow. This approach allows a rapid response to production questions when beginning a new simulation project. The methodology was applied to a cycle-time and capacity analysis of the photolithography operation for Siemens' Dresden wafer fab. The results of this simulation study are presented.