Secondary ion mass spectrometry is applied to the depth profiling of the superlattice active region of lattice matched (∼9.2 μm) Al0.48In0.52As/In0.53Ga0.47As/InP quantum cascade lasers. The developed measurement procedure is capable of characterizing the quality of each individual layer in the superlattice region, including layers as thin as 0.7 nm. The oxygen level for AlInAs and InGaAs layers is in the range of 1-3 × 1017 atms per cm3 and below the detection limit (∼1 × 1016 atms per cm3), respectively. Oxygen is not uniformly distributed in the AlInAs layers - more oxygen is embedded into the structure during the very first stage of the growth of the AlInAs layer and thus the corresponding interface is 1.83 ± 0.31 times more contaminated than the other. The procedure can also be operated in 3D imaging mode which proves to be invaluable for failure analysis.