Selective epitaxial growth of silicon through windows in SiO2 in a hot wall low‐pressure chemical vapor deposition system has been used to fabricate silicon‐on‐insulator structures by epitaxial lateral overgrowth. Under suitable conditions this process yields a continuous epitaxial film over buried oxides. However, a unique ‘‘seam‐like’’ defect was observed at the interfaces where two lateral growth fronts meet each other. A series of threading dislocations along the merging interface were identified as the structure of the seam defect. Epitaxial lattice mismatch at certain juncture points of two opposing growth fronts could have initiated the dislocations. Accumulated strain in the epitaxial film from oxide surface perturbation or interfacial stress are possible sources of the juncture point mismatch.