The early stage formation of a GaAs-Ge(110) interface has been analysed by using a consistent tight-binding method that introduces charge neutrality conditions at the interface. Our analysis yields results consistent with the experimental information, showing that the interface is practically formed with the deposition of a monolayer of Ge. We conclude that the interface considered is an interesting example in which the models based on the concept of charge neutrality levels apply for, both, semiconductor-semiconductor and metal-semiconductor junctions.