The semiconductor manufacturers are actively competing with each other in the semiconductor foundry market around the world. Improving the cycle time can effectively shorten the time between the customer orders and make profit for the wafer Fabs. This study utilizes a Taiwanese semiconductor (A company) as a case study to develop a dispatching rule for photolithography machine in a wafer Fab. Because there is no dispatching rule in this company, the cycle time does not meet the requirements of it’s customers. Therefore, the object of this study is to apply the Design of Experiments (DOE) to develop an optimal dispatching rule for A company. The result of this study indicates that the cycle time of A company is significantly reduced by employing the proposed dispatching rule.