In Cognitive Radio Network (CRN) secondary users (SUs) opportunistically access the channel whenever it is not being used by primary users (PUs). The CRN Medium Access Control ( MAC) protocol needs to sense the channel to find out the availability of spectrum. In this paper we propose a hybrid sensing mechanism for SUs to access the channel in CRN environment. In the proposed hybrid sensing mechanism the SU sense the channel periodically when it is used by PU while the SU sense the channel continuously whenever the channel is used by the SU. We investigate the role of this hybrid sensing mechanism wherein PUs have a preemptive priority over SUs. Later we study the performance of our MAC protocol with respect to the following metrics: MeanWaiting Time (MWT) and Queue Length Distribution (QLD). We study the variation of these metrics as a function of sensing period (τ ), SU arrival rate (λs), SU service rate (μs), and PU traffic intensity rate (ρPU). From simulation results, we observe that there is a trade-off between MWT and sensing energy while considering periodic sensing. We finally suggest the type of sensing mechanism to be used for the channel access, based on the traffic intensity of PU. © 2017 IEEE.