N-type GaAs/Ga0.4Al0.6As heterostructures have been grown on semi-insulating GaAs substrates using metal-organic chemical vapour deposition. The GaAs layers were mounted on insulator supports and the substrates and Ga0.4Al0.6As removed using a preferential etching procedure. The preparation and electrical properties of submicrometre thick insulator-supported n-type GaAs layers are described.