AbstractCritical heat flux (CHF) tests on a new type of rectangular cooling tube, ‘saw-toothed fin duct, SFD’ for high heat flux components were performed under one-sided heating conditions. The tube has internal triangle fins at the heating side to enhance the CHF characteristics. Hydraulic conditions were as follows: axial flow velocity ranged from 2 to 12 m/s. Local pressure at the center of the test sample was 1 MPa and inlet water temperature was 21–25 °C. In the present work, SFD, which has a fin height of 3.46 mm and an installation angle of the fin of 70°, results in the highest CHF of 43 MW/m2 at the axial flow velocity of 10 m/s. This value is 1.3 times higher than that obtained with a Hypervapotron.