The effects of two‐step annealing, rapid thermal annealing (RTA) followed by furnace annealing (FA), on the crystalline and electrical properties of buriedn‐type layers formed in (100) Si by As implantation at an incident energy of 1 MeV have been investigated. The crystalline properties have been examined by Rutherford backscattering measurements and by transmission electron microscopic observations. The electrical properties have been studied by differential Hall measurements. A comparison between the annealing process of two‐step annealing and that of RTA or FA alone is made. The experimental results obtained from this work clearly show that buriedn+layers without residual defects can be formed by the use of RTA at 1050 °C followed by FA at 1000 °C, and that they are difficult to be formed by one‐step annealing of FA or of RTA.