This article presents a computational study of saturated flow boiling in non-circular microchannels. The unit channel of a multi-microchannel evaporator, consisting of the fluidic channel and surrounding evaporator walls, is simulated and the conjugate heat transfer problem is solved. Simulations are performed using OpenFOAM v2106 and the built-in geometric Volume Of Fluid method, augmented with self-developed libraries to include liquid-vapour phase-change and improve the surface tension force calculation. A systematic study is conducted by employing water at atmospheric pressure, a channel hydraulic diameter of µm, a uniform base heat flux of , and by varying the channel width-to-height aspect-ratio and channel fin thickness in the range –4 and , respectively. The effects of conjugate heat transfer and channel aspect-ratio on the bubble and evaporative film dynamics, heat transfer, and evaporator temperature are investigated in detail. This study reveals that, when the flow is single-phase, higher Nusselt numbers and lower evaporator base temperatures are achieved for smaller channel aspect-ratios, from and when , to and when , for same fin thickness . In the two-phase flow regime, Nusselt numbers in the range are achieved. The trends of the Nusselt number versus the aspect-ratio are non-monotonic and exhibit a marked dependence on the channel fin thickness. For small fin thicknesses, and , an overall ascending trend of for increasing aspect-ratios is apparent, although in the narrower range –2 the Nusselt number appears weakly dependent on . For thicker fins, and , the Nusselt number decreases slightly when increasing the aspect-ratio in the range –2, although this trend is not monotonic when considering the entire range of aspect-ratios investigated. Nonetheless, due to conjugate heat transfer, Nusselt numbers and evaporator base temperatures follow different trends when varying the aspect-ratio, and channels with seem to promote lower evaporator temperatures than higher aspect-ratio conduits.