The lattice parameters of heavily boron doped silicon homoepitaxial layers before and after rapid thermal annealing at different temperatures (800–1100 °C) are characterized by x‐ray double crystal diffraction. The results illustrate that although the strain relaxation occurs after the rapid thermal annealing (RTA) treatment, the improvement of the crystalline quality of epitaxial layers are observed at RTA temperatures higher than 1000 °C. The proportional relationship between the lattice mismatch and the substitutional boron concentration with the lattice contract coefficient &bgr;=5.3 (in units 10−24cm3) is valid up to the concentration of 3×1020cm−3. ©1995 American Institute of Physics.