Doping phenomena and the diffusion of dopants in thin Si films on insulator structures were evaluated. As and BF, were implanted into three kinds of Si-on-insulator (SOI) substrates (with differing top-Si and Si/buried-oxide (BOX) interface qualities) and a Czochralski-grown (Cz) Si substrate. The As and B profiles before and after annealing were measured by secondary ion mass spectroscopy, the carrier profiles were evaluated by spreading resistance measurement, and some of the structures were observed by transmission electron microscopy. Arsenic atoms piled up at the top-Si/BOX interface in each SOI substrate. The amount piled-up depended strongly on the quality of the Si/BOX interface. No significant pile-up was observed at the interface in the B profiles; however, the height of the B subpeak near the depth of the end-of-range defects strongly depended on the SOI fabrication technique. It is proposed that the quality of the SOI crystal and the Si/BOX interface, which varied with the fabrication technique, affected the dopant profiles.