A heat radiating unit is provided on a front face with at least one raised strip having a curved head portion and a neck portion, the neck portion being located at a joint of the raised strip and the heat radiating unit and having a width smaller than that of the curved head portion; and on a reverse face with at least one receiving groove opposite to the raised strip, the receiving groove having a curved recess portion and an engaging shoulder portion, and the engaging shoulder portion being located at a joint of the receiving groove and the heat radiating unit. A plurality of the heat radiating units can be assembled to provide a heat sink by engaging the curved head portion and the neck portion of one heat radiating unit with the curved recess portion and the engaging shoulder portion, respectively, of another heat radiating unit.