Abstract: Advances in integrating and packaging technologies have enabled electronic products which are increasingly small, multifunctional and high-powered. High heat flux dissipation becomes one of the key issues to be solved in packaging designs. Compared with traditional cooling technologies, microchannel heat sinks can be directly integrated in the device/system substrates through processing methods compatible with the current mainstream manufacturing processes. The built-in design of the heat sinks can greatly shorten the heat transfer path and largely enhance the cooling effectiveness. Therefore, this cooling technique is particularly suitable for the thermal management of high-density microsystems. The characterization quantities, the influence factors and enhancement methods of heat and mass transport in the microchannel heat sinks are reviewed. Optimizing the microchannel structure and using high-performance coolant, for example nanofluids, are the important ways to improve the overall cooling performance of the microchannel heat sinks. However, there are still many challenges in fabricating complex three-dimensional microchannel structures and controlling the stability and performance of nanofluids. Further research on the manufacturing technology and heat and mass transport mechanisms will help to expand the practical application of the microchannel cooling technique in thermal management of high-density microsystems.