Lattice strain due to boron in silicon epitaxial wafers has been measured by the x‐ray double‐crystal technique. It is found that the lattice strain depends on the crystal orientation and that the strain for (100) is about 1.3 times larger than that for (111). The results for (111) lead to a lattice contraction coefficient for boron &bgr;=8×10−24cm3/atom, which is 1.5–4 times larger than previous values obtained with diffused (111) wafers.