An exemplary heat sink assembly includes a heat sink and a clip resiliently clamping the heat sink on a printed circuit board. The heat sink includes a base and a plurality of first fins and two central second fins extending upwardly from the base. The clip includes a locating portion fixed between the second fins of the heat sink, a pair of elastic portions extending outwardly from opposite ends of the locating portion and oriented towards substantially opposite directions, and two hooks extending outwardly from ends of the operating members, respectively. An acute included angle is formed between each elastic portion and the locating portion of the clip in an original relaxed position, and the acute included angles become approximately right angles when the clip is preassembled in the heat sink with the elastic portions abutting the second fins.