A heat sink assembly includes a heat sink (20), a clip (40), and a spring clamp (60). The heat sink includes a base (21), pin fins (23), and slots (25, 27) defined between respective adjacent rows of the pins in perpendicular crisscross fashion. The clip made from a flexible metal wire includes a central body (41) with a raised portion (43), and two arms (45) extending perpendicularly but in different directions from opposite ends of the body. A hook (47) is formed at a free end of each arm. The spring clamp includes an elongate central pressing portion (61). A longitudinal opening (63) defined in the pressing portion engagingly receives the raised portion. Two pairs of elastically deformable wings (65) extend from respective opposite sides of the pressing portion. The clamp is resiliently retained in corresponding slots of the heat sink, and thus secures the clip to the heat sink.