Material properties of GaAs films grown on Si(321) substrates using molecular beam epitaxy (MBE) were evaluated and compared to films grown on Si(100) and Si(211). Dislocation densities in the GaAs(321) films, determined using transmission electron microscopy (TEM), were lower than those observed in GaAs(100) and GaAs(211), and the density of stacking faults in GaAs(321) also was quantitatively lower than in GaAs(211). Low-temperature (4.2 K) photoluminescence spectroscopy (PL) indicated that the tensile stress on the GaAs(321) films was greater than that on GaAs(100). These differences are attributed to changes in the strain-relaxation process caused by variations in the number of geometric arrangement of active-dislocation glide systems with different orientations. In addition, Si uptake near the GaAs/Si interface was less than 1/100 of a monolayer in GaAs(321) and 1/4 of a monolayer in GaAs(100). This difference is attributed to the presence of a non-polar (neutral) interface in the (321), whereas the (100) has a polar (charged) interface. MODFET devices with a I-)m gate length exhibited a transconductance of 180–200 ms/mm, comparable to devices on homoepitaxial GaAs(100).