•Thermal performance of a copper made microchannel heat sink is investigated.•Silver nanoparticles are synthesized and used in the cooling loop.•37% enhancement in overall thermal performance of the system is reported.•Small penalty for friction factor and pressure drop is reported.•Fouling was found to reduce the thermal performance of the system. Thermal performance of a copper-made heat sink with rectangular microchannel was assessed within laminar flow regime. Silver nanoparticles were synthesized and dispersed into the deionized water as a potential coolant. Pressure drop, friction factor, heat transfer coefficient and fouling thermal resistance parameter of the system were experimentally investigated for mass concentrations of 0.01%, 0.05%, and 0.1%. Results showed that the heat transfer coefficient of the microchannel is enhanced when deionized water (as a traditional coolant) is replaced with the nanofluid. Importantly, a small increase in pressure drop, friction factor and fouling thermal resistance parameter were reported when nanofluid is used in the system. With an increase in the flow rate and mass concentration of nanofluid, the heat transfer coefficient and pressure drop of the Microchannel Heat Sink (MCHS) increased. Likewise, the local heat transfer coefficient and overall thermal resistance of the microchannel decreased along with the length of the microchannel. The highest heat transfer coefficient (as a thermal performance index) was also seen in the entrance region of the microchannel. The highest value for the fouling thermal resistance parameter was observed for the highest mass concentration of nanofluid which was 1.07 for wt.% = 0.1. The flow rate of fluid was found to enhance the fouling thermal resistance parameter over the 1000 min of the operation. Despite the enhancement in the fouling thermal resistance parameter and friction factor, there was an optimum concentration for silver-water nanofluid in which the overall thermal performance of the system was maximized such that the overall thermal performance of the system can be enhanced up to 37% at Reynolds number 1400 and at wt.% = 0.05.