In this paper a method has been proposed to improve the performance of NoCs by prioritization of packets generated in the processing cores of the network. Packets generated from the processing cores with large amount of output network traffic get a higher priority compared to the packets generated from cores with ordinary output network traffic. When there is contention in an output port, the packets with higher priorities are sent first. We have prioritized packets in all ordinary applications in order to improve the performance of the NoC. Simulation results on different real traffic patterns show that when the traffic pattern of the NoC is not uniform, our method achieves a significant improvement in performance while adding a low area overhead to the arbiter of the network switch. In addition, to efficiently design the proposed arbiter, a model in gate level is presented.