Power electronics is limited in its operational capabilities due to increasing heat flux densities, generating large thermal stresses and hotspots within the devices. Failure mechanisms are exacerbated by excessive temperature rises, which must be controlled. Heat-pipes have already demonstrated their ability to treat localized hotspots and to transfer high heat flux densities to the heat-sink. The cooling efficiency can be improved by a better integration of electronics and heat-pipes. Polymer-based heat-pipes offer many advantages: they are lightweight and can be mass-produced at low cost with good integration possibilities. However, the thermal conductivity of polymers is much lower than that of metals, increasing the thermal resistance between the junction and the cooling medium. Technologies such as 3D Plastronics and 3D Printing allow to address this issue, at least at the prototyping stage before considering mass-production. 3D Plastronics is a combination between the polymer processing and electronics, offering a solution to integrate electronic circuits on the 3D polymer objects surface. Stereolithography 3D printing creates 3D shaped polymer materials with acceptable properties (chemical resistance, operating temperature, mechanical properties). In this research, we propose a novel approach to fabricate 3D-printed polymer-based heat-pipes intended for GaN transistors. Two designs are presented and characterized: (i)heat-pipes fabricated entirely with polymer, (ii)heat-pipes fabricated using a hybrid polymer/copper technology. The electronic copper circuit on the polymer surface is created using plastronics technology. The first tests performed with the fluid HFE7000, show that the fluid/wall heat transfer coefficient can reach 9500 W/m².K in hybrid polymer/copper heat-pipes against 400 W/m².K for polymer heat-pipes. Moreover, the high flux densities that can be dissipated (> 50 W/cm²) in design (ii) are compatible with the targeted medium power applications. The metallized circuit has adequate electrical conductivity. In conclusion, our preliminary experimental results with the hybrid design compare very favorably with those in the literature.