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To address the thermal management challenges associated with high power dissipation devices, we describe a novel hybrid thermal management device that enables significant enhancement of conventional air-cooled heat sinks using on-demand and spatially controlled droplet/jet impingement evaporative cooling. The device architecture modifies an air (gas)-cooled heat sink by adding a multiplexed, planar microelectromechanical system (MEMS)-based droplet ejector array as a capping surface of the finned structure of a conventional heat sink. Such a minimal modification of the heat sink allows one to exploit high heat flux evaporative cooling by virtue of delivering streams of liquid droplets or jets to the highly thermally conducting heat-spreading surface of the heat sink fins. The phase change associated with liquid droplet evaporation results in significant (~ 50%) enhancement of the dissipated thermal load, beyond what could be achieved by using air (gas) cooling alone. Finally, among the additional key attractive features of the described technology is its ease of implementation (i.e., modification of commercially available heat sinks), paving the way to power-efficient, low-cost thermal management of high power dissipation devices.