Abstract: High power semiconductor laser arrays (bars) have been widely used in many fields. Thermal stress induced by mismatch of thermal expansion coefficients between the bar and heat sink leads to smile effect. Larger smile can induce a lower beam quality which causes difficulty in collimation of laser beam. Thermal uniformity of the bar can be achieved by reducing temperature of the intermediate light emitting unit caused by thermal crosstalk. This paper presents the optimization of heat sink structure for temperature uniformity of the bar. Graphene on copper foil (GCF) with high thermal conductivity and two symmetrical holes (each beside an end of the foil) are adopted to optimize the traditional conduction cooled semiconductor (CS) heat sink. Numerical simulations on the thermal behavior of the CS-packaged bar show that, when the GCF foil is 8 mm long, the temperature difference is reduced from 7.94 ℃ to 3.65 ℃; the through holes cause temperature rise of emitters on both sides of the bar, and the temperature difference is further reduced to 3.18 ℃.