The O center substitutional to As (O-As) is addressed through hybrid functional calculations as a candidate defect to explain the Fermi-level pinning in oxygen-doped GaAs. The defect center shows amphoteric behavior which could lead to Fermi-level pinning. However, the calculated charge transition levels only moderately agree with the experimental pinning level. Furthermore, the first-neighbor shell of the O atom and the absence of negative-U behavior clearly contrast with the experimental characterization. Thus, the present results do not support the O-As center as origin of the observed Fermi-level pinning in oxygen-doped GaAs. (C) 2013 Elsevier B. V. All rights reserved.