A heat sink includes a base plate and a plurality of cylindrical pins extending upwardly from the base plate. The cylindrical pins each include an upper dissipating portion, a lower mounting portion, and an engaging portion between the dissipating portion and the mounting portion. The mounting portion is interferentially fitted in a lower part of a corresponding aperture of the base plate. The engaging portion has a diameter smaller than that of the mounting portion. The engaging portion is cramped by an interior wall of the base plate defining an upper part of the corresponding aperture of the base plate by punching an upper surface of the base plate downwardly at a rim of the corresponding aperture.