A heat sink assembly (10) includes a heat sink (12) and a wire clip (14). The heat sink includes a base (120) and a plurality of fins (124) mounted on the base. A channel (126) is defined between two neighboring ones of the fins. A pair of points (1250) are punched on one of the fins and received in the channel. The wire clip includes a main body (140), first and second legs (141, 142) extending from opposite ends of the main body. The wire clip intervenes across the points and extends through the channel such that the main body is received in the channel and the first and second legs are located at opposite ends of the channel. Thus, the wire clip is prevented from dropping from the channel in a direction parallel to the channel.