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Junction-to-fluid thermal resistivities R''jf, of two dual-side-soldered insulated gate bipolar transistor (IGBT) modules immersion cooled in a hydrofluoroether C3F7OCH3 liquid were measured experimentally. R''jf = 0.040°C·cm2/W for 0.144 cm2 die at a peak heat flux of 1180 W/cm2 and 55 A, and 0.11 °C· cm2/W for 1.46 cm2 die at a peak heat flux of 550 W/cm2 and 305 A. A technique for automatic in situ degassing that would reduce manufacturing cost and permit field servicing of immersion systems that reach subambient pressure when idle showed fluid loss rates of 0.3 g per 100 cm3 of air vented, roughly 1/100th that expected from an HFC-134a air conditioning system with a similar leak. Experiments to quantify packaging density and fluid requirements suggest that 100 cm3 of fluid is required to dissipate 1 kW and packaging density is limited only by the electrical bus geometry.