Ga₂O₃/GaAs heterojunctions are emerging as promising candidates for next-generation power electronics, photonics, and energy devices, leveraging the high breakdown voltage and thermal stability of Ga₂O₃ alongside the mature technology, high hole mobility, and higher refractive index of GaAs. The efficiency of these devices depends strongly on the band alignment between the two materials, however both type-I and type-II alignment have been reported in the literature for these heterostructures. To address this ambiguity, we use hybrid density functional theory to systematically investigate the band alignment at GaAs/Ga₂O₃ interfaces, focusing on the role of interface chemistry. By considering Ga-O-, As-, and As-O-rich interfaces both in amorphous and crystalline Ga₂O₃ phases, we demonstrate that interface stoichiometry determines the alignment type: Ga-O-rich interfaces exhibit type-II alignment with large valence band offsets ( 3.1 eV), while As-rich and As-O-rich interfaces favor type-I alignment with reduced offsets ( 2.3-2.6 eV). These trends are attributed to interface dipole formation driven by bonding configuration. Our findings provide insight into the relationship between chemistry and band alignment in GaAs/Ga₂O₃ heterostructures, enabling targeted optimization for specific device applications.