Optical transitions between quantum well subbands have large oscillator strengths and narrow linewidths so that they can be used for the detection of infrared light. Here we show that the intersubband separation can be varied over a wide energy range by depositing a thin barrier layer of AlGaAs in the middle of a GaAs well. In a sufficiently narrow well it should be possible to push the subbands out of the well, i.e., perform the transition from the quasi‐two‐dimensional case to the quasi‐three‐dimensional case.