In order to meet increased demand for dissipating high heat fluxes from electronic chips that are continually shrinking in size, development of new cooling technologies have been considered for the last two decades. Recent research efforts have shown that boiling two phase flow through the mini-channels can provide desired heat transfer coefficients. The occurrence of the dryout phenomenon followed by a sudden increase in temperature due to the critical heat flux is one of the most important challenges in this context. In this study, departure from nucleate boiling phenomenon due to the critical heat flux in a mini-channel has been examined using computational fluid dynamics. The governing equations solved are generalized phase continuity, momentum and energy equations. Wall boiling phenomena are modeled using the baseline mechanistic nucleate boiling model developed by Rensselaer Polytechnic Institute (RPI). To simulate the critical heat flux phenomenon, the RPI model is extended to the departure from nucleate boiling (DNB) by partitioning wall heat flux to both liquid and vapor phases considering the existence of thin liquid wall film. It was observed that by applying high heat fluxes near to CHF, DNB occurred and a vapor layer formed adjacent to the wall while most of the flow field is still subcooled liquid.