In this work, we studied the flow boiling of dielectric liquid FC-72 in a flat microchannel 66 µm high and 10 mm wide. Heating was carried out by a thin-film ITO heater, which was in direct contact with the working fluid. Flow regimes were studied in a wide range of liquid flow rates. It is shown that the flow regimes in a flat microchannel differ significantly from the flow regimes in round and rectangular mini- and microchannels. The boiling curves are constructed. The dependence of the heat transfer coefficient on the heat flux for various regimes of two-phase flow has been studied.