The resistivity and mobility of carbon-doped GaAs nanowires have been studied for different doping concentrations. Surface effects have been evaluated by comparing unpassivated with passivated nanowires. We directly see the influence of the surface: the pinning of the Fermi level and the consequent existence of a depletion region lead to an increase of the mobility up to 30 cm(2)/Vs for doping concentrations lower than 3 x 10(18) cm(-3). Electron beam induced current measurements show that the minority carrier diffusion path can be as high as 190 nm for passivated nanowires. ((c) 2013 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim)