In this paper, a new type of hybrid solar cell based on a heterojunction between poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and vertically aligned n-type GaAs nanowire (NW) arrays is investigated. The GaAs NW arrays are fabricated by directly performing the nano-etching of GaAs wafer with spun-on SiO(2) nanospheres as the etch mask through inductively coupled plasma reactive ion etching. The PEDOT: PSS adheres to the surface of the GaAs NW arrays to form a p-n junction. The morphology of GaAs NW arrays strongly influences the characteristics of the GaAs NW/PEDOT: PSS hybrid solar cells. The suppression of reflectance and the interpenetrating heterojunction interface of GaAs NW arrays offers great improvements in efficiency relative to a conventional planar cell. Compared to the planar GaAs/PEDOT:PSS cells, the power conversion efficiency under AM 1.5 global one sun illumination is improved from 0.29% to 5.8%.