As a result of the increasing size and complexity of embedded systems, object-oriented techniques are going to be adopted in the embedded software development. In embedded software developments, we have to consider nonfunctional requirements such as real-time properties and resource requirements. To deal with these requirements, some methodologies design the system using a thread-based approach. In such approach, we need to extract threads from the concurrent objects defined in the analysis model. However, current methodologies do not provide enough support to do so. In this paper, we propose a formal approach to extract threads from concurrent objects. We also present an experimental application of the proposed approach to the development of a device driver.