Using a microchannel heatsink is an advanced cooling technique to meet the cooling needs of electronic devices installed with high-power integrated circuit packages (microchips). These heat sinks utilize microchannel heat exchangers (MCHEs) with boiling-mode cooling (BMC) and nanofluids. Such MCHEs usually have high operating pressures (3-13 bar). In spite of a large number of studies carried out on other thermo-physical properties of nanofluids, few studies have been carried out on the latent heat of evaporation (LHE) of nanofluids. The limited published literature all reports the LHE under atmospheric conditions, which are outside of the operating range of MCHEs. The precise estimation of the LHE is essential for the appropriate design of MCHEs. In the present study, a novel experimental setup is applied for the measurement of LHE under high operating pressure and temperature conditions (90-180 °C and 80-880 kPa) and for investigating the effects of pressure on the LHE. It has been shown that by exposing a nanofluid under pressure some new hydrogen bonds are formed increasing the LHE, which significantly improves the performance of boiling cooling of MCHEs. Based on the obtained results by pressurizing a 2 vol% (4.6 wt%) SiO2 nanofluid, the LHE can be increased by about 17% in comparison with that of a similar non-pressurized sample. On the other hand, pressurization can improve nanofluid stability. Finally, a correlation is proposed for the calculation of enthalpy of evaporation of SiO2 nanofluids.