The spectrum scarcity issue due to a fixed radio spectrum allocation system has become an obstacle to future wireless communications. In cognitive radio, the idea of an open spectrum was devised, which allows unlicensed users to utilise these underutilised licensed spectrum bands opportunistically. Several synchronisation‐based, Medium Access Control protocols for cognitive radio networks have been reported. This study examines how these protocols suffer from the common control channel bottleneck problem in a dense network. The analysis shows that control messages exchanging in a fixed channel negotiation window in the control channel is not efficient in dense cognitive radio networks. This increases the channel access delay and limits the network performance. This study develops an analytical model to calculate the expected channel access delay and analyse the impact of the number of nodes on the channel access. The analysis is verified with simulations. Copyright � 2012 John Wiley & Sons, Ltd.