The interference oscillations in normal‐incident Fourier‐transform infrared (FTIR) spectra of AlSb/GaSb superlattices, which disturb the observation of intersub‐band transitions, have been theoretically simulated and experimentally measured. Both theoretical and experimental results show that on GaSb substrates, interference oscillations are relatively weak when using GaSb rather than AlSb as the buffer layer; and by contrast, on GaAs substrates, they are weak when using AlSb rather than GaSb as the buffer layer. Using an AlSb buffer on semi‐insulating GaAs substrates, normal‐incident intersub‐band transitions fromL1toL2sub‐bands in AlSb/GaSb superlattices have been observed by the usual FTIR technique. ©1995 American Institute of Physics.