Abstract. Much has been said about the importance of formal verification in hardware synthesis, but little has been done. Where it has been applied at all, it has only been used on simple, idealized examples. This paper describes the application of formal semantic analysis and verification to part of a working high-level synthesis system. The process revealed several significant errors in that system, errors that had previously been undetected. This experience leads to some reflections on the need for a rigorous, formal basis for hardware specification and synthesis, and on the value of formal techniques.