Ion beam mixing and damage production at GaAs-AlAs interfaces was studied by Rutherford backscattering and channeling methods. It was observed that the general features of the intermixing of GaAs with AlAs at 100K are typical of that in other semiconductor and metallic systems but that the damage production is not. The GaAs layers amorphize at a very low ion dose whereas the AlAs layers are very resistant to amorphization. Damage in the AlAs begins at one interface of the GaAs and grows through the AlAs layer, but damage at the other interface never nucleates. The ratio of nuclear to electronic stopping influences the growth of the damage zone.