Software process improvement holds a significant promise to reduce cycle times and provide greater value to all development activities involved in the software process development. While these methods appear to be well suited for embedded systems development, their use has not become an organized practice. In the same way as that of software development, the embedded systems development could be failing due a bad management in the development process. CMMI-DEV v1.2 is a process improvement maturity model that has been developed by the Software Engineering Institute at Carnegie Mellon. CMMI-DEV v1.2 defines “what” processes and activities need to be done and not “how” these processes and activities are done. In this paper we introduce the SPIES methodology that integrates the CMMI-DEV v1.2 Level 2 process areas to specify a process for developing embedded systems. This methodology incorporates the TSP principles to support the lack of management and improve the process specification. To illustrate this approach, we describe an experimental system in which it has been applied to develop and manage a traffic light system.