Abstract: A heat sink having an assembling device using mechanical characteristics of resilience or flexibility so as to effectively fasten a heat sink. In one embodiment, this invention comprises a chassis having a heat dissipating surface, a plurality of fastening holes formed on the chassis, and fastening bolts and helical springs corresponding to the fastening holes, wherein the fastening bolts each further comprise a mushroom-shaped insertion end. In another embodiment, the heat sink comprises a chassis having a heat dissipating surface and a fastening seat for fastening the heat sink, wherein the fastening seat is formed of a resiliently curvable and integrally formed sheet and is provided with a pair of hooks each having a V-shaped barb for inserting the invention into holes abutting the chip and pre-formed on a motherboard and for resiliently pressing the heat sink against the chip.