The zinc dopant concentration and distribution in GaAs nanowires is quantified by atom probe tomography. Material deposited radially by a vapour-solid process is shown to have a significantly higher dopant concentration in comparison to the core which grows by the vapour-liquid-solid process. Zinc concentrations of up to 7×10¹⁹ and 5×10²⁰ atoms/cm³ are measured for core and shell materials respectively. Dopant activation is confirmed by electrical characterization which demonstrates an orders of magnitude increase in nanowire conductivity.