Air-based convective cooling of electronic components is facing a dual challenge: (i) an increasing cooling demand and (ii) a drive towards weight reduction. For many electronic components, plate-fin heat sinks are chosen to dissipate the generated heat. The first objective (i) can be approached using shape optimisation, however, the weight-saving objective (ii) remains difficult to meet with solid heat sinks. A vapour chamber heat sink can provide both cooling enhancement, due to the internal phase change heat transfer, and weight reduction by removing solid material. This study compares the thermal characteristics of a traditional plate-fin heat sink and a vapour chamber heat sink of identical external dimensions, cooled by forced air convection in a cross-flow configuration. An experimental setup has been built to investigate the effect of the following parameters: the air flow Reynolds number on the external heat transfer from the fins; the type of fluid and vapour chamber filling ratio on the power range which can be dissipated; and finally the choice of heat sink material due to its direct influence on both weight and conduction resistance. Finally, a model is proposed to calculate the overall thermal resistance, including heat spreading, internal boiling, two-phase transport and condensation, and the fin resistances, taking into account the different parameters studied. These findings are used in combination with an ongoing numerical study on shape optimisation of similar plate-fin heat sinks.