Scheduling semi-conductor manufacturing process systems is a complicated and difficult job due to such characteristics as reentry into manufacturing processes, high uncertainty of processes, and products and technologies changing rapidly. They have carried out many studies to find the efficient ways for semi-conductor manufacturing systems with a view to accomplishing the goals of systems like saving cycling time and increasing production quantity per unit time. The production flow in the semi-conductor industry has the most unique characteristics and makes it difficult to plan production and to schedule semi-conductor manufacturing. Currently, the scheduling methods in semi-conductor assembly processes follow the dispatching rule by simple FCFS(first come first serve). And backlog is operated as a buffer based on daily production quantity. In this study, therefore, we will apply various dispatching rules by real time basis and verify the effect and result of exact scheduling through simulation, based on the assumption that competitive advantages in production come from efficient inventory control and exact scheduling.