A method of making a heat pipe includes the steps of: providing a mandrel, a capillary wick and a straight tubular shell; inserting the mandrel and the capillary wick into the shell; cramming powder into the shell, wherein the powder can be sintered between the shell and the mandrel; sintering the shell having the mandrel, the capillary wick and the powder therein; and drawing the mandrel out of the shell and filling working media into the pipe, and vacuuming and sealing the pipe. The mandrel defines a longitudinal slot therein, and the capillary wick is positioned in the slot.