To evaluate the crystallinity of hetero-epilayers by the double crystal rocking curve (DCRC), the ZnTe epilayers were grown on the GaAs (1 0 0) substrate by hot wall epitaxy. The thermal pre-heating temperature and the substrate temperature were investigated for the optimum growth of the ZnTe epilayers by the values of the full width at half maximum (FWHM) of the DCRC, The FWHM of the DCRC was the smallest at the pre-hearing temperatures of around 510 and 590 degreesC, while the largest at 550 degreesC. And it was found that the optimum substrate temperature for the ZnTe/GaAs epilayers was 390-400 degreesC. The values of the FWHM of the DCRC of the epilayers decreased with increasing thickness of the epilayers. The ZnTe lattice constants perpendicular to the interface were measured as a function of the substrate temperature and the film thickness. From the results obtained, it was found that the lattice constant was smaller than that of the bulk ZnTe due to the large thermal tensile strain caused by the large difference in thermal expansion coefficients between the substrate and the epilayer. The (4 0 0) ZnTe epilayer rocking curve width dependence of the (4 0 0) GaAs substrate rocking curve width was investigated.