HighlightsCarbon fiber (CF) scaffolds with horizontally aligned, diagonally aligned and vertically aligned structure were fabricated via magnetic field-assisted Tetris-style stacking and carbonization process.The obtained CF scaffolds/ polydimethylsiloxane composites showed ultrahigh thermal conductivity (above 40 W m−1K−1) in the fiber alignment direction.Fibers with different alignment direction can be combined by multiple stacking and carbonization process, allowing for the efficient heat transfer along customized paths.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40820-023-01119-0.