The development of heat sinks for microelectronic applications, which are compatible with sustainable development, involves the achievement of a subtle balance between a superior thermal design, minimum material consumption, and minimum pumping power. Due to the rapid proliferation of electronic systems, substantial material streams and energy consumption rates are associated with the cooling of computers, as well as other categories of electronic equipment. This presentation explores the potential for the least-energy optimization of natural- and forced-convection cooled rectangular plate heat sinks. The results are evaluated in terms of a heat sink coefficient of performance, relating the cooling capability to the energy invested. Guidelines for "sustainable" heat sink designs are suggested.