We designed and synthesized 4-dodecyloxybenzenediazonium tetrafluoroborate (1), which preferentially reacts with metallic single-walled carbon nanotubes (SWNTs) by kinetic control. We first determined the suitable experimental conditions for the preferential reaction of 1 with individually dissolved SWNTs by monitoring the decrease in absorbance for the metallic SWNT in the range of 400–650 nm in the absorption spectrum of the SWNTs. The reacted SWNTs were thoroughly rinsed with THF to obtain THF-insoluble SWNTs. The Raman spectrum of the THF-insoluble SWNTs showed a strong peak near 180 cm−1, which corresponds to a semiconducting breathing band. The metallic breathing bands (≈220 cm−1) and Breit–Wingner–Fano (BWF) modes (1520 cm−1) corresponding to the metallic SWNTs were much weaker than those of the pristine SWNTs. We also confirmed that metallic peaks in the range of 400–650 nm in the absorption spectrum of THF-insoluble SWNTs that were individually dissolved in an aqueous micelle of sodium cholate were almost nondetectable. All the results indicate that the THF-insoluble SWNTs are semiconducting.