A cooling device includes two side boards and a memory device is clamped between the two side boards. A cooling unit is positioned above the two side boards by two clips and includes a plurality of fins. A heat conduction member is connected with the cooling unit and inserted into a slot defined in one of the two side boards so as to directly in contact with the memory chips of the memory device. The heat is directly conducted to the heat conduction member and can be dispensed by the fins of the cooling unit.