The fabrication of planar p-n junctions in GaAs by Be ion implantation is described and the properties of these junctions are compared with Zn-implanted and Zn-diffused diodes. The Be-implanted diodes exhibit good forward characteristics, very low reverse leakage current, and high breakdown voltage. It appears that lateral diffusion is negligible in this fabrication method, suggesting that such junctions may be used in GaAs integrated circuit applications.