The Microfluidic, Extreme heat flux, CMOS compatible, Heat-exchanger (MECH-X) is an embeddable siliconbased reactor-style heat sink which has been experimentally studied by the authors. The 800 mu m thick MEMS heat sink discretizes the working fluid into stacked primary and secondary chambers to enhance phase change heat transfer. Piranha Pin-Fin (PPF) microstructures-reported previously by the authors- have been employed in the primary reaction chamber. The PPF structures vent higher-enthalpy fluid into a secondary, or booster, chamber for additional heat transfer. The MECH-X system has been shown to dissipate heat loads exceeding 10,000,000 W/m(2) with dielectric fluid HFE7000 while maintaining surface temperatures below 95 degrees C. The present work reports on flow boiling experiments performed to characterize system-level performance of the MECH-X heat sink at mass fluxes of 680, 1440, and 3350 kg/s/m(2). HFE7000 was used as a coolant at ambient lab temperature (similar to 23 degrees C) and a system pressure of 377 kPa. A 3.95 mm(2) heating element, which simulated a heat generating component, was maintained below 95 degrees C with heats loads exceeding 1 kW/cm(2). Experiments were terminated at this heat flux due to saturating a 50 V-Dc laboratory power supply. Results are also presented at a system pressure of 239 kPa, and results are compared to first generation PPF heat sinks. (C) 2018 Elsevier Ltd. All rights reserved.