Hybrid systems made up of a continuous plant supervised by a discrete - event controller are considered in this paper. A set of optimal feedback control functions is defined at the continuous level. The aim of the discrete - event controller, modelled by means of a finite-state automaton, is that of choosing, in the above mentioned set, the best control action to be applied to the plant in dependence of the current plant conditions and of possibly occurred external events (hence, the overall control scheme can be viewed as a two-level hybrid control scheme). An invariance property of the hybrid control scheme is proved and extensive simulation results are reported, showing the effectiveness of the proposed methodology.