Semiconductor manufacturing process is becoming more and more complex while manufacturing technology is developed to deep sub-micron region. Therefore, more and more company is turning to capital-light and focusing on core business. Foundry is the player usually providing silicon manufacturing service to customers. According to customer's capital-light strategy, foundries are required to provide more and more services out of silicon manufacturing, such as design service, silicon validation, assembly, and testing service. This is known as turnkey service. Foundries usually do not have their own assembly capacity. To ensure packaged product quality, a robust assembly subcontractor quality management system is very important for foundry. This paper will discuss on how to build up quality management system of subcontractor development, monitoring, and driving to continuous improvement.