The robust design of one-side-heated plasma-facing components and other high heat flux components is dependent on knowing the local distribution of inside wall heat flux in the flow channels. The local inside wall heat flux can be obtained from selectively chosen local plasma-facing component wall temperatures close to the inside boundary of the flow channel. To this end, three-dimensional thermal measurements for a one-side-heated monoblock were made and show: (1) the three-dimensional variation of the wall temperature close to both the heated and fluid/solid surface boundaries, (2) the resultant effects of mass velocity on the three-dimensional wall temperature/outside heat flux relationship, and (3) the occurrence of local critical heat flux and local post-critical heat flux. The monoblock has a 180.0 mm heated length, has a 10.0 mm inside diameter, and has a square cross-section with 30.0 mm nominal outside surfaces. Published by Elsevier Ltd.