Numerical and analytical methods are employed to investigate the thermal and fluid flow performance of a microchannel heat sink for cooling a high-power diode laser bar. Heat transfer characteristics and pressure drop in the microchannel under different flow rates are studied. A thermal resistance network, which is proved to have less than 5.4% error, is proposed to characterize the resistance components for the microchannel heat sink. Both numerical modeling and thermal resistance network analysis are verified by experimental results based on the wavelength shift method. Two new heat sinks with more uniform temperature distribution for laser emitters compared with the existing design are presented, and their performance is validated by numerical modeling and spatially resolved spectrum measurements. (C) 2019 Optical Society of America