Facing the problems of high thermal resistance and high temperature difference on the top surface of semiconductor laser arrays′ directional macro-channel liquid-cooled heat sinks inducing different lifetimes and hard controlling of spectral width, the temperature distribution of internal heat sinks through the finite element modeling is presented. The heat sink under consideration is made of copper with varying the area of coolant inlet. Established analysis and simulation models show that a heat sink with smaller inlet area provides a lower surface temperature gradient and a better capability of heat dissipate. A continuous wave (CW) 120 W output semiconductor laser arrays pump source (3 laser bars) is obtained by using this kind of small inlet macro-channel heat sink. The central wavelength is 807.7 nm with a full wavelength at half maximum (FWHM) of 2.8 nm.