Blocking　of　new　arriving　services　and　dropping　of　ongoing　services　are　inherent　problems　in　Cognitive　Radio　Networks　(CRNs),　which　need　to　be　addressed　to　enhance　spectrum　efficiency.　In　particular,　Secondary　Users　(SUs)　undergo　service　degradation　in　the　face　of　Primary　Users　(PUs)＇　arrivals.　In　this　paper,　we　present　a　scheme　called　Efficient　Spectrum　Utilization　(ESU)　that　reduces　the　dropping　and　blocking　probabilities　of　existing　and　new　services,　respectively,　to　make　efficient　use　of　the　available　spectrum.　The　scheme　divides　the　available　spectrum　into　reserved　and　non-reserved　bands.　The　reserved　band　is　dynamically　allocated　a　number　of　channels　from　the　non-reserved　band　in　order　to　accommodate　those　services　which　face　interruptions　while　operating　in　the　non-reserved　band.　The　scheme　renders　dynamic　access　to　the　available　spectrum　and　facilitates　priority-based　channel　allocation　and　termination.　SUs　are　divided　into　low　and　high　priority　levels　depending　on　their　Quality　of　Service　(QoS)　requirements.　SUs　with　low　priority　level　are　granted　direct　access　to　both　the　bands　to　enhance　channel　utilization.　SUs　operating　in　the　reserved　band　with　high　priority　levels　are　granted　uninterruptible　status　to　ensure　a　certain　level　of　service　provisioning　to　SUs.　The　proposed　ESU　scheme　is　modeled　using　Continuous　Time　Markov　Chain　(CTMC)　and　mathematical　expressions　are　derived　for　several　QoS　parameters.　Performance　of　the　proposed　scheme　is　evaluated　under　various　network　conditions.　Results　demonstrate　that　ESU　reasonably　improves　spectrum　efficiency　under　channel　failure　in　CRNs.　(C)　2020　Elsevier　B.V.　All　rights　reserved.