GaAs/Ca//0//. //4//3Sr//0//. //5//7F//2/GaAs ((100) and ( OVER BAR 1 OVER BAR 1 OVER BAR 1)) SOI structures were fabricated by using MBE growth. The SOI-GaAs layers were investigated by He ion channeling and backscattering spectroscopy (RBS) and Nomarski optical microscope. It was found that the temperature dependences of the crystalline quality and the surface morphology were different between the layers on (100) and OVER BAR 1 OVER BAR 1 OVER BAR 1) substrates. The channeling minimum yield ( chi //m//i//n) of 5. 5% was obtained in a layer grown on the ( OVER BAR 1 OVER BAR 1 OVER BAR 1) substrate using a two-step growth technique.