Dynamic spectrum sharing among the wireless users is growing demand to increase the spectrum usage. In this paper,, based upon a pricing strategy to overcome the drawbacks of the traditional mechanisms. The proposed mechanism enhances the spectral efficiency of the cognitive users and also motivates the primary users to lease the bands to the cognitive users, with increased primary user revenue. Fairness among cognitive users is also ensured in this mechanism.. Simulation results show that our mechanism increases the spectral efficiency of cognitive users and the revenue of primary users.