This brief investigates the security control for a class of networked discrete-time semi-Markov jump systems subject to round-robin protocol. Considering the deception attack and round-robin protocol, observer-based security control scheme is first established in a unified framework. By fully taking into account the variations of Lyapunov function at the switching instants and non-switching intervals, sufficient conditions are developed to ensure the $\sigma$ -error mean-square stability for networked semi-Markov jump systems. Then, the controller and observer parameters are co-designed by resorting to a set of linear matrix inequalities. Finally, the F-404 aircraft engine model is illustrated to validate the theoretical results.