Wide-Band-Gap semiconductors have enabled considerable miniaturization of power devices, which requires, however, new thermal management solutions to handle the resulting high heat fluxes. Recently, embedded liquid cooling in GaN-on-Si devices was demonstrated as a promising solution by flowing a coolant through microchannels etched in the silicon substrate. However, its impact on power devices’ electrical characteristics, especially at high voltage, is yet to be investigated, which is crucial to assess the viability of the technology. Besides, previous demonstrations were limited to relatively low-power devices, while embedded liquid cooling for high-current and high-voltage (650 V) commercial GaN transistors would show the full potential of the technology. Here, we integrate embedded liquid cooling on 650 V, 50 mΩ GaN-on-Si commercial power devices. We demonstrate no negative impact on the device dc or switching performance due to the embedded liquid cooling, which proves the robustness and validity of the technology. Besides, liquid-cooled devices show more than 4× higher current capability and much-improved RON × Eoss figure-of-merit in a large output current range compared to forced-convection air-cooling, highlighting their potential for high-current applications. Finally, deionized water and a dielectric fluid (3M Novec 7200) are compared as coolants, revealing a trade-off between thermal performance and reliability during high-voltage operation.