High quality ZnTe epilayers on (1 0 0) GaAs substrates have been successfully grown by hot wall epitaxy. The strain in the hetero-interface has been studied by four-crystal X-ray diffraction and transmission electron microscopy (TEM). The smallest FWHM value of the four-crystal X-ray rocking curve was 66 aresec, which is the best so far value reported. On the other hand, the reciprocal lattice mapping indicates a splitting of the (4 0 0) peaks from the GaAs substrate, indicating the existence of a strained region in the substrate. A TEM study confirms that the strain exists not only in the ZnTe epilayers but also in the GaAs substrate near the interface. This is the first such direct observation for the case of ZnTe/GaAs. (C) 2002 Elsevier Science B.V. All rights reserved.