Experiment were carried out to investigate the heat transfer characteristics of an aluminum foam block as a porous heat sink on a heat source by a vertical air jet impingement that can be applied for electronics cooling. The performance of the aluminum foam heat sink was evaluated by the convective heat transfer coefficient on the heat source. At a fixed porosity, pore density ($eta$) of the foam and Reynolds number Re were varied in the range of $eta$a=10, 20, 40 PPI(Pore Per Inch) and $850leqReleq25000$. A nozzle diameter and the nozzle-to-plate spacing were also varied. It was found that the convective heat transfer was enhanced by the aluminum foam heat sink with lower pore density due to relatively intensified flow through the foam block. The aluminum foam block with much reduced weight shows slightly better performance with larger Nusselt number, compared with the convectional heat sink.