High‐resolution transmission electron microscopy and selected area electron diffraction have been used to study Hg0.8Cd0.2Te wafer. Two kinds of chemical composition modulated structures were found. One is a one‐dimensional modulation with modulated wave vectorq*=(a*−b*)/5.6 and the other two‐dimensional modulation with modulated wave vectorsq1*=(a*−b*)/5.6 andq2*=(a*−b*)/11.2−0.22c*. Both structures have a common modulated wavelength of 2.54 nm. ©1995 American Institute of Physics.