A heat sink includes a plurality of metal fins interconnected together. Each metal fin includes a main plate, a flange extending forwardly from the main plate and an interlocking unit formed on the flange. The interlocking unit includes an engaging ear and a hook. The ear extends rearwards from a rear edge of the flange and defines a locking hole therein. The flange defines a cutout adjacent to a front edge thereof. The cutout is aligned with the ear and recessed rearwards from the front edge of the flange. The hook extends forwardly from the flange and is located within the cutout. The ear of a fin is engaged in the cutout of an adjacent rear fin. The hook of the adjacent rear fin is engaged in the locking hole of the engaging ear of the fin.