In this paper, we evaluate the productivity performance of Taiwanese semiconductor companies using a three-stage Malmquist DEA panel model to account for external environmental effects on firms' managerial performance over time. The empirical results have shown that the effects of external environments on firm's efficiency performance are significant. Based on the empirical results of the proposed panel model with the adjusted inputs, in general we conclude that the semiconductor industry in Taiwan has enjoyed efficiency improvement, technical progress and productivity growth in 2002-2007. However, we also find that without considering the effects of the environmental factors, the evaluation of firms' changes in productivity and technology will be overestimated for the semiconductor industry, whereas the efficiency improvement will be mostly underestimated.