A heat dissipating device includes a heat sink and a clip attached on the heat sink. The heat sink includes a solid trunk and a plurality of fins extending radially outwardly from a circumference of the trunk. A rectangular extension portion is formed at a bottom end of the trunk. A pressing portion extends from the extension portion and abuts against the clip toward the heat sink in an axial direction of the heat sink. The clip defines a rectangular opening fittingly receiving the extension portion to thereby form a positioning structure for preventing the clip from moving relative to the heat sink in a circumferential direction of the heat sink.