In this paper, three dimensional two phase flow with vaporization has been numerically studied in a mini-channel heat sink. The modeling of the two phase flow was achieved using the Volume of fluid method. The geometric reconstruction scheme, that is based on the piecewise linear interface calculation method was applied to reconstruct the liquid-vapor interface. For an accurate modeling, the effect of axial conduction has been also taken into account, using a conjugate heat transfer model. The vaporization was modeled by developing a numerical code for which appropriate source terms have been added in the momentum and energy equations to take into account heat absorption during vaporization or heat release during condensation. The developed numerical procedure has been validated by the comparison of the obtained results for vaporization inside a cylindrical tube with the correlation given in the literature. A good agreement has been reached between the heat transfer coefficient calculated and that obtained by the used correlation, especially for higher positions along the tube for which the flow regime is well established and disturbances due to the entrance effects disappear. Some typical results are also displayed and discussed. The obtained results show the evolution of the vapor fraction from the inlet of the heat sink to its outlet where all the liquid becomes a vapor. The obtained results of both vapor fraction and velocity contours showed the benefit of such numerical procedure in representing the phase change in heat sinks.