Conventional double-layered microchannel heat sink (DL-MCHS) significantly improves temperature uniformity on the bottom wall due to temperature compensation between the two layers through conduction. However, temperature of the top coolant is always higher than that of the bottom coolant in the inlet region of bottom channels, which inevitably leads to a heating effect of the top coolant on the bottom coolant. To prevent the heating effect, a new DL-MCHS with truncated top channels was proposed in our previous study. To further enhance the cooling performance of the new design, multiparameter optimizations are performed at various fixed pumping powers Omega and fixed coolant volumetric flow rates Q(v), respectively. The optimization algorithm is composed of a three-dimensional solid-fluid conjugate heat sink model and a simplified conjugate-gradient method. Overall heat resistance R is the objective function to be minimized with channel number N, channel height H-c, channel width W-c, and the dimensionless truncation length of top channels I as search variables. With a constant heat flux of 100W cm(-2) applied to the bottom wall, and a constant Omega of 0.05 W, the optimal design has N = 55, W-c = 0.116 mm, H-c = 0.525 mm, l = 0.28, and R = 0.102 K W-1. However, with a constant Q(v) = 200 ml min(-1), the optimal design has N = 79, W-c = 0.026 mm, H-c = 0.175 mm, I = 0.38, and R = 0.093 K W-1. The improvements of cooling performance for constant Omega and constant Q(v) are all attributed to the enhancement of cooling effect and/or the reduction of heating effect. Finally, the design directions of the four search variables are given at various Omega and Q(v). (C) 2015 Elsevier Ltd. All rights reserved.