A parametric optimization of a novel hybrid configuration of liquid-cooled heat sinks is presented herein. Such a hybrid design encompasses a combination of channels and microjets for optimal performance of chip scale high-power density electronic packages. Fractal flow channel geometries were used to create variants consisting of 16, 32, and 64 channels and a corresponding number of microjets in the impingement cavity. In addition to the conventional coplanar setup, where channels and area enhancing features align with the main flow direction, an out-of-plane network of channels was created to allow for removal of the cooling fluid in the opposite direction of the impinging jets. The parametric analysis was performed via 3-D CFD simulations to investigate the tradeoff between hydraulic and thermal resistances in jet cooling systems. The thermal resistance of the heat sinks was estimated and the pressure losses were calculated for every design. Observations of the flow patterns were used to inform on the optimization process of the architecture of the flow channels. A metric able to merge thermal and hydraulic performance was defined, such that the thermo-fluid characteristics of a liquid cooled heat sink are represented using one parameter. The utilization of this parameter led to a unique performance assessment of the proposed hybrid liquid-cooled heat sinks and allowed to identify an optimum design, which yields the lowest thermal resistance with minimum pumping power input. (C) 2019 Elsevier Ltd. All rights reserved.