Abstract Unique methods of preventing the interfacial reactions between GaAs and EuBa2Cu3O7−y (EBCO) films are presented. When GaAs is deposited on clean EBCO surfaces, photoelectron spectroscopy results show that considerable reduction of EBCO and hard oxidation on Ga and As take place at the interface even at room temperature (RT). In order to suppress these interfacial reactions, either an AsOx or SrF2 layer is applied as a “functional” interlayer. Therefore, one monolayer of an AsOx or SrF2 interlayer is formed on EBCO, effectively decreasing the GaAs/EBCO interfacial reactions at RT. We find that when EBCO substrates are annealed at 220°C to crystalize GaAs, the SrF2 interlayer has a stronger suppressing effect than AsOx.