A silicon on insulator device has a silicon layer (10) over a buried insulating layer (12). A nickel layer is deposited over a gate (16), on sidewall spacers (22) on the sides of the gate (16), and in a cavity on both sides of the gate (16) in the silicon layer (10). A doped amorphous silicon layer fills the cavity. Annealing then takes place which forms polysilicon (40) over the sidewall spacers (22) and gate (16), but where the nickel is adjacent to single crystal silicon (10) a layer of NiSi (44) migrates to the surface leaving doped single crystal silicon (42) behind, forming in one step a source, drain, and source and drain contacts.