The interfacial behavior of the bonded p-GaP/n-GaAs wafers, with activated surfaces, that use an Ar fast atom beam was investigated. The bonding strength of the interface was 9.8 MPa at room temperature, and the GaP was fractured and remained on the GaAs following the tensile test. Two amorphous layers with identical thicknesses of 3.5 nm were found across the interface without annealing. When annealing was executed, the electrical current-voltage characteristics improved and the amorphous layers diminished across the interface. The amorphous layers adjacent to the GaP across the interface are attributed to the Ga-rich layer because of the depletion of P.