We propose a formal real-time semantics for UML statecharts aimed at the requirements level. A requirements-level model assumes perfect technology and has a considerably simpler semantics than an implementation level model. Our semantics is an adaptation of the Statemate statechart semantics, with local variables, real time, identifier addressing, point-to-point communication, synchronous communication and dynamic object creation and deletion. We start with an informal comparison of Statemate and UML statechart semantics and then give a formalisation of our semantics in terms of labelled transition systems.