We have applied high-resolution chemical imaging in a transmission electron microscope to study compositional variations across an InGaAs/InAlAs double quantum well structure in the (100) orientation. The structures of interest are grown on an InP support and consist of two 40 Å layers of InGaAs separated by 20 Å of InAlAs. For this(InGa)x(InAl)1−xAssystem, we have obtained compositional information with an accuracy of about 20&percent; and a maximum spatial resolution of1/4unit cell. The results clearly show compositional irregularities on a monatomic scale. ©1997 American Institute of Physics.