To support the continuing Defect Engineering activities in the Infineon Mask House, a professional analysis tool has been developed for Defect Yield Management, in collaboration with EGsoft. EGSoft is the software division of Electroglas Inc. and suppliers ofthe YieldManager TM product, used for Yield Management in numerous wafer fabs. The requirement for such a tool was catalysed by the ever-increasing demand for sophisticated defect analysis, to accelerate defect learning and the identification of major and minor defect-related-yield detractors. Yield Mask consists of a database, which centrally stores all relevant information from Defect Inspection, Repair and Review tools in the Infineon Mask House and an analysis tool, which allows users to analyse the data collected on their PC. The analysis tool can be divided into six major modules: Data Set Builder, Mask Map, Map Gallery, Image Gallery, Charting and Customise: The functionality of the above-mentioned modules is presented and their application in the analysis of defect data demonstrated. The tool is shown to be an invaluable, cost-effective labour-saving device in a high-end Mask House, where the time required to analyse and resolve defect problems can be dramatically reduced.