A method for making a heat dissipating device includes the steps of: preparing a container body that has a fluid passage and opposite upper and lower walls, the fluid passage being in fluid communication with an inner space in the container body; vacuuming the inner space through the fluid passage; filling the inner space with a predetermined amount of a working fluid through the fluid passage; and depressing a wall portion of a selected one of the upper and lower walls in such a manner that the depressed wall portion is deformed toward the other of the upper and lower walls so as to form a depression in the selected one of the upper and lower walls, and so as to form a sealing mechanism that functions to isolate the fluid passage from the inner space.