A high-resolution, high-sensitivity VG x-ray photoelectron spectrometer was used to study a semiconductor layer structure grown for the fabrication of resonant tunneling bipolar transistor devices. Depth profiling using argon ion milling, at a rate of 50 Angstrom/min, has allowed the device layers to be identified on the basis of their elemental composition. The measurement system sensitivity was sufficient to identify the elemental components of the 11 Angstrom AlAs barrier layer in quantum tunneling InGaAs/AlAs device layers.