The high power density of emerging electronic devices is driving the transition from remote cooling, which relies onconduction and spreading, to embedded cooling, which extracts dissipated heat on-site. Two-phase microgap coolersemploy the forced flow of dielectric fluids undergoing phase change in a heated channel within or between devices. Such coolers must work reliably in all orientations for a variety of applications (e.g., vehicle-based equipment), as well as in microgravity and high-g for other applications (e.g., spacecraft and aircraft). The lack of acceptable models andcorrelations for orientation- and gravity-independent operation has limited the use of two-phase coolers in suchapplications. Previous research has revealed that gravitational acceleration plays a diminishing role in establishing flow regimes and transport rates as the channel size shrinks, but there is considerable variation among the proposed microscale criteria and limited research on two-phase flows in low aspect ratio microgap channels. Reliable criteria for achieving orientation- and gravity-independent flow boiling would enable emerging systems to exploit this thermal management technique and streamline the technology development process.