We present the results of secondary ion mass spectroscopy studies of silicon nanowires doped with phosphorus by thermal diffusion. First, silicon nanowires were grown on the surface of single-crystal silicon wafers with a polished and ground surface using method of metal-assisted chemical etching. Doping of nanowires with phosphorus atoms by thermo diffusion method occurred at temperatures of 900-980 ° C during 15-40 minutes. Secondary ion mass spectroscopy was used to study the distribution of phosphorus atoms over the depth of nanowires, impurity distribution dynamic profiles were calculated for the samples obtained on the polished and ground surfaces of silicon wafers. Analysis of the dynamic profiles of the secondary ion mass spectroscopy for the distribution of Si-P compounds in samples of doped silicon nanowires revealed that the maximum concentration of phosphorus atoms in such samples is localized predominantly in the nanostructured layer, and a very small amount diffuses into the bulk silicon layer. The estimated depth of occurrence of the dopant in silicon nanowires is about 1300 nm.