A cooling device incorporating a boiling chamber includes a heat sink (10), a fan (30) and a fan duct (50) covering the heat sink and the fan therein. The heat sink includes a chamber (14) receiving liquid (26) therein and a mounting plate (16) located at a bottom surface (200) of the chamber. The fan duct is mounted to two opposite edges of the mounting plate. The fan is mounted in a front part while the heat sink is mounted in a rear part of the fan duct. A top wall (220) of the chamber has a plurality of fins (18) extending upwardly therefrom. The liquid has a level higher than that of a bottom surface of the top wall so that a constant contact between the liquid and the top wall is ensured.