Arsenic and boron implanted MoSi 2 layers as diffusion source for the formation of n + /p and p + /n ultra-shallow junctions, respectively, are investigated. The high arsenic diffusivity and solubility in MoSi 2 , as well as the favorable arsenic segregation coefficient at the silicide silicon interface, make Mo-silicide suitable as arsenic diffusion source and allow the formation of n + /p junctions as shallow as 100 nm with high surface carrier concentration. On the contrary, the low boron mobility in MoSi 2 , probably due to boron-molybdenum compounds, make ineffective the Mo-silicide as boron diffusion source.