A cooling system for removing heat from a heat generating component, includes a base (100) and a heat sink (200) mounted on the base. The base includes a lower portion and a higher portion surrounding the lower portion. The lower portion and the higher portion cooperatively define a space (18) receiving working fluid therein. The heat sink defines an evaporating passage (252) and two condensing passages (254) located at two opposite sides of the evaporating passage. These passages are in fluid communication with the space. Cooperatively the space and the passages define a loop for circulating the working fluid therein. The working fluid has a phase change for dissipating heat generated by a heat-generating electronic component. A wick structure (400) is received in the space.