A high-volume epitaxial reactor has been used to investigate the feasibility for the production growth of GaAs on silicon substrates. The reactor is a customized system which has a maximum capacity of 39 three-inch diam wafers and can accommodate substrates as large as eight inches in diameter. The MOCVD materials growth technique was used to grow GaAs directly on p-type, (100) silicon substrates, three and five inches in diam. The GaAs surfaces were textured with antiphase boundaries. Double-cyrstal rocking curve measurements showed single-crystal GaAs with an average FWHM of 520 arc seconds measured at four points over the wafer surface. Within-wafer thickness uniformity was plus or minus 4% with a wafer-to-wafer uniformity of plus or minus 2%. Photoluminescence spectra showed four peaks at 1. 500, 1,483, 1. 464, and 1. 440 ev. Schottky diodes were fabricated on the GaAs on silicon material.