Silicon nanowires (SiNWs) have considerable potential to assist the realization of next-generation metal-oxide semiconductor field-effect transistors (MOSFETs) with vertical structures. Impurity doping and its control is a key technique in the creation of SiNW devices, which renders it necessary to develop characterization methods for dopant atoms in SiNWs. In this Research News, we described how the states of the dopant atoms boron and I phosphorus can be detected.