Transmission electron microscopic observations have been made on 100‐keV phosphorus‐implanted silicon layers with a dose of 5 × 1014/cm2as a function of implantation temperature and the subsequent annealing treatment. The annealing behavior of secondary defects is strongly dependent upon the implantation temperature. Also, the nature of dislocation loops formed in the implanted layers shows implantation temperature dependence: dislocation loops in room‐temperature implanted layers are predominantly interstitial in nature, whereas in layers implanted at higher temperatures than 500 °C they are predominantly of vacancy type, and both types of loops coexist in 200–400 °C implanted samples.