Heat transfer and fluid flow in a novel class of water-cooled milli-channel heat sinks are investigated. The heat sinks are manufactured using an extrusion freeform fabrication (EFF) rapid prototyping technology and a water-soluble polymer material. EFF permits the fabrication of geometrically complex, three-dimensional structures in non-traditional materials. Silicon carbide, SiC, is TEC-matched to silicon and is an ideal material for heat exchangers that will be mounted directly to heat dissipating electronic packages. This paper presents experimental results on the heat transfer and flow in small SiC heat exchangers with multiple rows of parallel channels oriented in the flow direction. Rectangular heat exchangers with 3.2 cm 2.2 cm planform area and varying thickness, porosity, number of channels, and channel diameter were fabricated and tested. Overall heat transfer and pressure drop coefficients in single-phase flow regimes are presented and analyzed. The per channel Reynolds number places the friction coefficients in the developing to developed hydrodynamic regime, and showed excellent agreement with laminar theory. The overall heat transfer coefficients for a single row SiC heat exchanger compared favorably with a validation heat exchanger fabricated from copper, however the heat transfer coefficient in multiple row heat sinks did not agree well with the laminar theory.