An experimental study of saturated flow boiling in a high-aspect-ratio one-side-heating rectangular microchannel is conducted with deionized water as the working fluid. The bottom surface of the microchannel is constructed of two different material, one is the untreated hydrophilic silicon wafer with a contact angle of 65° ± 3°, the other is the super-hydrophilic silicon wafer deposited with a thin film of 100-nm-thickness silicon dioxide through PECVD with a contact angle less than 5°. The heat transfer characteristics of saturated flow boiling in the microchannel is studied and the flow pattern is photographed with a high speed camera. It is found that the heat transfer mechanism is dominated by convective evaporation, the heat flux transfers through the conduction and convection in the thin liquid film and evaporation at the interface between the vapor and liquid. The thinner the liquid film, the greater the heat transfer coefficient. The local dryout phenomenon is observed on the untreated hydrophilic surface while the super-hydrophilic surface can restrict the occurrence of local dryout phenomenon. This study proposes the modified Li (2010) correlation as a formula for calculating the heat transfer coefficient.