We report on the mixed photovoltaic/photoconductive operation mode of a visible blind photodetector based on GaN nanowires containing a p-i-n junction. The photodetector operates as a photovoltaic device close to zero bias and exhibits a photoconductive gain (>100) for biases above vertical bar V vertical bar > 2 V. We show that this unusual behavior of a p-i-n photodiode is specific to the case of nanowires. The gain is attributed to the illumination-induced modulation of the width of the depleted region at the nanowire lateral surface allowed because of the specific nanowire geometry with the p-i-n junction orthogonal to the lateral nanowire surface. (C) 2014 AIP Publishing LLC.