A heat sink fixing device has an enclosing frame socket having a central part for disposing a heat generating unit of an electronic device thereon, with a heat sink mounted on the enclosing frame socket and covering the heat generating unit. A first fixing part is provided on a bottom surface of the heat sink, and a second fixing part corresponding to the first fixing part of the heat sink is provided on the enclosing frame socket, allowing the heat sink to be coupled to the frame socket by coupling the first fixing part of the heat sink with the second fixing part of the frame socket, thereby substantially maximizing heat dissipating area on the heat sink.