A heat sink includes a fin assembly (20) including a plurality of fin plates (22) and a fan (30) mounted on the fin assembly. Each fin plate includes a plurality of cutouts (226) defined on one edge thereof, and the cutouts of the fin plates cooperatively form a scraggy surface when the fin plates are assembled together. Airflow produced by the fan directly impinges on the scraggy surface thereby enhancing heat transferring between the fin plates and the airflow.