Deformation characteristics and interfacial adhesion property of silicon nitride/gallium arsenide film/substrate systems were investigated by use of nanoscratch. During scratching, three different types of deformation, elastic, elastoplastic and fracture, were discovered. The critical loads for film failure were obtained. The critical loads, together with the other scratch parameters, were used to determine the interfacial adhesion energies. The practical adhesion energies per unit area of the bilayers obtained were 2.72 and 3.73 Joules/m2, respectively. The tensile stress developed just behind the contact area and at the interface was attributed to the film failure. It was also found that residual compressive stress strengthened, but tensile stress weakened, the interfacial adhesion.