Cognitive Radios are a key to implementing dynamic spectrum access (DSA) wherein a secondary user (SU) can opportunistically access the licensed spectra of a primary user (PU). This paper proposes a new QoS aware MAC protocol with an aim at providing differential transmission opportunities to different traffic classes in Cognitive Radio Networks (CRN). We achieve this by varying parameters like AIFS, CWmin, CWmax in a manner similar to IEEE 802.11e. Through extensive simulation using MATLAB we study important metrics such as (i) mean delay, (ii) jitter and (iii) saturation throughput of SUs by varying (a) number of SUs, (b) SU packet length and (c) mean OFF duration of the PU (spectrum opportunity). We also study the effect of PU on number of RTS/CTS collisions and number of SU data packets dropped. Although simulation study shows a behavior is similar to 802.11e peculiarities of CRN lead to interesting results. © 2014 IEEE.