The effect of a magnetic field on structural properties during anodization of GaAs substrates was investigated to gain insight into formation of ordered hole arrays on GaAs surfaces. Lorentz force induced by a magnetic field considerably affected formation of honeycomb hole arrays. In anodization with a magnetic field parallel to the surface, regularity of honeycomb holes was increased by increasing the magnetic field. The size of honeycomb holes also increased with increased magnetic field. The cross-sectional shape of holes anodized with a magnetic field parallel to the surface was asymmetrical, and the holes were shallow. For the sample anodized with a magnetic field perpendicular to the surface, the shape of holes was symmetric, and the holes were deep.