The diffusion of In in Si was investigated at 800 to 1000C by using secondary ion mass spectroscopy and transmission electron microscopy. The data indicated that, for implants at 150keV through a thin (19nm) oxide layer, the amount of dopant that left the Si was controlled only by the flow of In which reached the surface, being both the segregation coefficient at the SiO2/Si interface and the In diffusion coefficient in the oxide favorable to the out-diffusion. A comparison of experimental and simulated profiles showed that, besides the expected transient enhanced diffusion which occurred in the early phases of the annealing, a heavy loss of dopant by out-diffusion was associated with a high In diffusivity near to the surface. Measurements of the hole concentration in uniformly doped Si on insulator samples performed at 700 to 1100C indicated that the In solubility was equal or greater than 1.8 x 1018/cm3. This value was higher than those previously given in the literature.Investigation on Indium Diffusion in Silicon. S.Solmi, A.Parisini, M.Bersani, D.Giubertoni, V.Soncini, G.Carnevale, A.Benvenuti, A.Marmiroli: Journal of Applied Physics, 2002, 92[3], 1361-6