Abstract Electrical properties of the wafer bonding p-GaAs/n-GaN, p-GaAs/n-Si and p-GaAs/ITO//ITO/n-Si are investigated systematically by scanning Kelvin probe force microscopy (KPFM), capacitance–voltage ( C – V ) and current–voltage ( I – V ) measurements. By using KPFM, the contact potential distributions and contact barrier differences of these bonding heterojunctions with Schottky-like characteristics or ohmic feature have been obtained. The contact barrier differences measured by KPFM match well with those measured by C – V . These barriers indicate the thicker interface layer has a larger barrier height, which could contain more interface states. The I – V curve of the heterostructure with the smaller contact barrier difference is shown as an Ohmic contact feature. In contrast, the I – V curve of the junction with the larger contact barrier difference shows a Schottky contact behavior with a larger turn-on voltage. These behaviors indicate that the electrical conductivity of the bonding sample depends on the bonding interface layer significantly.