A novel porous heat sink with reentrant microchannels has been developed by traditional sintering fabrication method. It features 14 parallel Omega-shaped reentrant microchannels with a hydraulic diameter of 786 mu m. Two-phase boiling heat transfer performance of the reentrant porous microchannels (RPM) was evaluated to explore the feasibility of the enhancement and application in heat sink cooling. Using deionized water as coolant, flow boiling tests were conducted at the inlet temperature of 33,60 and 90 degrees C, mass flux of 125-300 kg/m(2) s. Comparisons with solid copper microchannels of the same reentrant configuration were performed, and the test results show that the reentrant porous microchannels presented a significant decrease of the wall superheat for the boiling incipience, delay and mitigation of two-phase flow instabilities, and 2-5 folds enhancement in two-phase heat transfer coefficient at low to moderate heat fluxes. It was also found that during the flow boiling of the reentrant porous microchannels, nucleation boiling governed the heat transfer mechanism at low heat fluxes and vapor quality, while forced convective boiling associated with thin film evaporation dominated at moderate to high heat fluxes. Furthermore, the two-phase flow instabilities characteristics were also accessed for the reentrant porous microchannels. (C) 2013 Elsevier Ltd. All rights reserved.