Heat from a heat generating device such as a CPU is dissipated by a heat spreader containing a cycled two-phase vaporizable coolant. The coolant cycles inside a closed metal chamber, which has an upper section and a lower section. The lower section contains a wick layer, a part or parts of which serves as an evaporator. The upper section is composed of a set of channels. The channel walls contain a plurality of cut-off openings over the evaporator region to allow for vapor distribution efficiently. The liquid coolant in the evaporator is vaporized by the heat from the heat generating device. The coolant vapor can prevail in the channels by either directly entering the adjacent channels or indirectly through lateral conduits formed with the wall openings. The vapor condenses on the channel, walls to liberate latent heat which is then dissipated out through the top chamber wall. The condensed coolant is directly collected by the lower-section wick and further flows back to the wick evaporator by capillary action, thereby cycling the coolant.