Microchannel is one of several high-heat-flux removal techniques being used in electronic cooling. Double-layered microchannel heat sink (DL-MCHS) with counter current flow arrangement is found not only to be able to lower the thermal resistance of the heat sink, but also decrease the maximum temperature and streamwise temperature rise on the base surface compared with single-layered microchannel heat sink (SL-MCHS). The present paper numerically investigated the thermal resistance, pumping power and temperature distribution on the base surface of substrate of DL-MCHS in different microchannel parameters and flow conditions, so as to find the complicated relationship between the overall performance of DL-MCHS and its geometric parameters and flow conditions. The numerical results show that the optimal width ratio of DL-MCHS should be increased when the microchannel aspect ratio is increased. The effectiveness of increasing aspect ratio of microchannels on improving the overall performance of DL-MCHS is dependent on the pumping power provided. DL-MCHS with higher aspect ratio and smaller width ratio is suited to the situation when higher pumping power is provided. Compared with the situation with identical inlet velocity being assigned to the bottom and upper microchannels, adjusting the inlet velocity of upper channels to be smaller than that of bottom channels may result in the improvement of the overall performance of DL-MCHS at a given pumping power, especially when the given pumping power is lower. These strategies could be tried in the real application of DL-MCHS. (C) 2014 Elsevier Ltd. All rights reserved.