Abstract: This disclosure concerns micro-scale heat transfer systems. Some systems relate to electronics cooling. As one example a microscale heat transfer system can comprise a microchannel heat exchanger defining a plurality of flow microchannels fluidicly coupled to each other by a plurality of cross-connect channels. The cross-connect channels can be spaced apart along a streamwise flow direction defined by the flow microchannels. Such a configuration of flow microchannels and cross-connect channels can enable the microchannel heat exchanger to stably vaporize a portion of a working fluid when the microchannel heat exchanger is thermally coupled to a heat source. Microscale heat transfer systems can also comprise a condenser fluidicly coupled to the microchannel heat exchanger and configured to condense the vaporized portion of the working fluid. A pump can circulate the working fluid between the microchannel heat exchanger and the condenser.