High-efficiency thermal energy transportation technology and cooling technology are important concerns spanning consumer, industry, and transportation sectors. Heat pipes (HPs) have long been used as heat transport devices for removing heat from various electronic devices. A wide variety of type of heat pipes has been studied, with many being implemented. However, the heat transport efficiency has plateaued, without any innovative breakthroughs, thus not keeping pace with the rapid industrial evolution. This study is concerned with the highly efficient heat transport phenomena obtained when the working fluid filling ratio of a pulsating heat pipe (PHP) is made extremely low. Specifically, it is considered that dryout occurs when the filling rate of the working fluid below 20 vol% in PHP, but in this study, heat transport was confirmed to occur without dryout at 5 vol% and 10 vol%. The PHP consisted of a flat aluminum tube with 28 straight channels and a total length of 400 mm. The channel dimensions had a square cross-section of 1.26 mm on each side, and water was used as the working fluid. The experiment was conducted with the PHP installed only in the bottom heat mode. Chemical treatment is applied to the channel surface of the flat aluminum tube to change its wettability. It was also clarified that the heat transfer was extremely efficient compared to the conventional filling ratio of PHPs. The minimum thermal resistance of 0.021 K/W was obtained for a 400 mm long PHP. The temperature difference between the evaporating and condensing sections was shown to be less than 1.0 K.