•SiNW, SiMP, and SiNW/MP two-tier structure were employed to enhance immersion cooling of Novec 649.•Novec 649 possesses low global warming potential and therefore it is environmentally benign.•Compared to a plain SiO2 surface, the CHF and HTC could be enhanced by 30% and 455%, respectively, on the SiNW/MP surface.•This result suggests the efficacy of the SiNW/MP two-tier structure for enhancing immersion cooling. Continual increases in the functionality and miniaturization of electronic devices have resulted in a rapid increase in the power density of such devices. Thus, an efficient cooling technology is required to maximize heat dissipation and prevent electronic failure. Immersion cooling is a promising technique for the thermal management of high-power-density electronics. However, common working fluids in immersion cooling have high global warming potential, and the heat transfer performance of immersion cooling requires improvement to achieve efficient cooling of state-of-the-art high-power-density electronics. In this study, Novec 649, which has low global warming potential and a low boiling point, was applied as a working fluid for immersion cooling. A Si nanowire (SiNW) array, Si micropillar (SiMP) array, and Si nanowires on a Si micropillar (SiNW/MP) two-tier structure were employed to enhance boiling performance. The SiMP surface exhibited the highest critical heat flux (CHF) of 23.5 ± 1.3 W/cm2, whereas the SiNW surface exhibited the lowest CHF but a relatively high heat transfer coefficient (HTC). The SiNW/MP surface exhibited the highest HTC of 23611.7 ± 1586.2 W/m2 K and a relatively large CHF of 17.4 ± 1.2 W/cm2. Compared with a plain SiO2 surface, the CHF and HTC of the SiNW/MP two-tier structure could be enhanced by 30% and 455%, respectively. These results suggest that the SiNW/MP surface is effective for enhancing immersion cooling.