Korea has developed a liquid breeder blanket for the test blanket module (TBM) program in ITER with a helium-cooled molten lithium concept. Since ferritic martensitic steel is used as the structural material for the TBM first wall (FW), various joining methods have been developed with hot isostatic pressing in order to develop a TBM FW fabrication method. In this study, three small mock-ups were fabricated in order to develop and verify the manufacturing method of the TBM FW through the pressure and helium leak tests. They were successfully fabricated. After fabrication and checking the performance of the mock-ups, a 1/6-scale mock-up was fabricated with a 260-mm height, 444-mm width, and 435-mm depth, in which width and depth were preserved and the number of channels was reduced from 60 to 10. The mock-up has a U-type shape and ten channels with a size of 20-mm height and 10-mm width for cooling. A manifold for flow testing and high heat flux testing of the 1/6-scale mock-up was designed and fabricated to distribute fluid uniformly to the mock-up.