An investigation of imperfections due to selective‐area planar double diffusions ofn‐ andp‐type impurities on epitaxial silicon has shown that elastic and inelastic lattice strain exists at the edges of oxide windows. This strain may act as nucleation sites for precipitating metallic impurities. High‐surface‐concentration emitter impurities (phosphorus) cause residual, inelastic strains at oxide edges, while base diffusions (boron) normally cause elastic lattice strains. X‐ray transmission topography reveals both elastic and inelastic strains. Surface reflection x‐ray topography is slightly more sensitive than x‐ray transmission topography for detecting defects due to shallow phosphorus diffusion. Chemical etching techniques delineate line defects which are unresolved by x‐ray techniques. The line defects are confined to the emitter area and extend in ⟨110⟩ and ⟨112⟩ directions. Differences in the results obtained by both x‐ray techniques are discussed in terms of defects observed by etching techniques.