A heat sink with a collapse structure and a semiconductor device with the heat sink are proposed, in which the heat sink is in ladder-like shape due to a height difference formed between an extending portion and an body of the heat sink, and the body has at least one surface exposed to outside of the semiconductor package. The extending portion produces collapse deformation in response to stress from engagement of molds in a molding process, so as to prevent a semiconductor chip from being damaged by the stress. The heat sink directly attached to the chip allows heat generated by the chip to pass through the extending portion to the body of the heat sink, and then the heat can be dissipated through the exposed surface of the body to the outside of the semiconductor package, so as to improve the heat dissipating efficiency.