Using the channeling technique for locating foreign atoms in crystals, we have obtained direct experimental evidence of an irreversible motion of In and Tl atoms from substitutional to interstitial sites during the annealing of ion‐implanted silicon samples. Preliminary Hall measurements indicate that a corresponding transition fromp‐ ton‐type behavior also occurs in the same temperature region — viz. 525–575°C. Implantation conditions were 1–3 × 1014ions/cm2at 40 keV, with the substrate at 350–450°C to prevent lattice disorder from accumulating.