A method for fabricating semiconductor packages is disclosed, including mounting and electrically connecting a semiconductor chip onto a chip carrier; mounting a heat-dissipating structure on the semiconductor chip; placing the heat-dissipating structure into a mold cavity for filling therein a packaging material to form an encapsulant, wherein the heat-dissipating structure has a heat spreader having a size larger than that of the predetermined size of the semiconductor package, a covering layer formed on the, and a plurality of protrusions formed on edges of the covering layer that are free from being corresponding in position to the semiconductor chip, such that the protrusions can abut against a top surface of the mold cavity to prevent the heat spreader from being warped; and finally performing a singulation process according to the predetermined size and removing the encapsulant formed on the covering layer to form the desired semiconductor package. Also, this invention discloses a heat-dissipating structure applicable to the method described above.