Phosphorus‐doped emitters have been formed by either conventional diffusion or implantation, anneal, and drive‐in processes. Transmission electron microscopy and measurements of transistor characteristics were made to evaluate the two processes. Comparison of structures with similar dislocation densities indicated that the dislocations in the implanted structures penetrated the emitter‐base sidewall, whereas the dislocations in the diffused structure were confined to the emitter region. The transistor with extended dislocations exhibited high leakage current and excess popcorn noise generating.