A comparative study pertaining to the molecular beam epitaxial growth of GaAs directly on silicon‐on‐sapphire and (101̄2) sapphire substrates has been made. Thermal strain is significantly reduced in these heteroepitaxial GaAs films as compared with GaAs on silicon; however, the (111) GaAs epitaxy on nominal (101̄2) sapphire contains double‐position boundaries. Hall effect measurements and current‐voltage characteristics from metal‐semiconductor contacts show that GaAs grown on silicon‐on‐sapphire is superior to GaAs grown on (101̄2) sapphire under the experimental conditions employed.