A combination of dispatching rules to determine a sequence of jobs is often used for the scheduling of liquid crystal display or semiconductor manufacturing systems. Fab engineers determine weights ranging between 0 and 1 for dispatching rules, and the dispatching rules assign a value from 0 to 1 for each job. Then the weight given by the engineers and the value from each dispatching rule are multiplied and added for all rules, and the job that has the largest weighted sum is chosen to be processed on an idle machine. Hence, the weights of dispatching rules significantly affect the performance of fabs and should be determined carefully. This article proposes a sequential search method for finding a proper set of weights for dispatching rules to improve an objective value of the fab, such as increasing throughput or decreasing setup times. We use a decision tree approach and a hierarchical clustering method to efficiently search for weights in a short period of time by eliminating some sub-spaces that are less likely to have good objective values. The proposed method finds better weight sets than a random search method and a response optimization method in experiments.