We investigated the misfit dislocation nucleation in lightly boron-doped silicon epitaxial layers deposited by vapor-phase epitaxy at 1080 degrees C-1150 degrees C on heavily boron-doped substrates. The substrate resistivity was 4 m Ohm cm which produced a misfit of 1.5 x 10(-4) and the layer thickness was 10 mu m. An orthogonal array of (1 1 0)-type dislocations was observed at the interface, as determined by g.b contrast criteria using Lang transmission X-ray topography. The misfit dislocations were observed only around the wafer periphery and the misfit dislocation length was shorter in regions where both orthogonal (1 1 0) segments existed. The density of the misfit segments was determined at the interface by defect-etching. In regions where the misfits were observed, triple-axis X-ray diffraction measurements determined that the layers were measurably relaxed. The distribution of defects indicates that the wafer periphery possesses heterogeneous nucleation sites for misfit dislocation nucleation.