Heavily boron‐doped (Na≳1×1019cm−3)Si epilayers grown on (100)Si by molecular beam epitaxy are investigated using double‐crystal x‐ray diffractometry. The variation of the Si lattice constant as a function of boron concentration is obtained from a combination of (400) rocking curve analysis and secondary‐ion mass spectrometry measurements on uniformly doped epilayers. This result is then used to determine the concentration profile in nonuniformly doped structures via dynamical simulations of experimental x‐ray rocking curves. The structures investigated include apipidoping superlattice and the results are found to be in excellent agreement with secondary‐ion mass spectrometry depth profiles.