A thermosiphon for cooling an electronic device having a mean width of dimension “b” comprises a boilerplate having a top surface and including a plurality of pyramid shaped fins projecting upwardly from the top surface. The boilerplate also has a bottom surface for receiving the electronic device to be cooled. A plurality of spaced apart condenser tubes is mounted above the boilerplate such that the boilerplate and the condenser tubes define a vapor chamber therebetween for receiving a working fluid therein. A plurality of convoluted fins extends between each adjacent pair of condenser tubes.