study an optimal maintenance policy for the server in a queueing system. Customers arrive at the server in a Poisson stream and are served by an exponential server, which is subject to multiple states indicating levels of popularity. The server state transitions are governed by a Markov process. The arrival rate depends on the server state and it decreases as the server loses popularity. By maintenance the server state recovers completely, though the customers in the system are lost at the beginning of maintenance. The customers who arrive during maintenance are also lost. In this paper, two kinds of such systems are considered. The first system receives a unit reward when a customer arrives at the system and pays a unit cost for each lost customer at the start of maintenance. The second system receives a unit reward at departure, and pays nothing for lost customers at the beginning of maintenance. Our objective is to maximize the total expected discounted profit over an infinite time horizon. We use a semi-Markov decision process to formulate the problem and are able to establish some properties for the optimal maintenance policy under certain conditions.