Semiconductor industry is capital intensive and competitive, and thus efficiently utilizing resources to provide products and services is essential for maintaining competitive advantages. Knowing whether the resource is properly utilized is the foundation for future improvements and/or decision making. This study investigates the economic efficiency of fabrication facility (fab) operations. We develop a two-stage overall efficiency model, which clearly defines and explains the "real" performance of fab production operations and the non-production issues. The model provides an overall performance index while considering different aspects. A single performance index can be used to evaluate and rank the performance for period review. Factors affecting performance can be identified. Furthermore, according to a real case, an ex post relative efficiency analysis is conducted and the initial results are reported. The case study can help providing diagnosis for inefficient production facilities and identifying best practices of efficient production units.