In the present chapter, semi-Markov models of systems of different profiles are built. In Section 6.1, the model of a loss queuing system is considered. In Section 6.2, the model of the system with cumulative time reserve is built. In Section 6.3, the model of two-phase system with a buffer stock is built. Approximate values of the system stationary characteristics are obtained. In Section 6.4, the model of technological cell with nondepreciatory failures is studied.