Oxide interfaces are attracting considerable interest owing to their rich and complex physics. One of the most widely studied phenomenon is the formation of two-dimensional electron gas (2DEG) at oxide interfaces, showing potential and promise for oxide electronics and possible device applications. 2DEG formation was originally thought to occur only at epitaxial interfaces, but recent work showed that 2DEG formation is possible with amorphous oxides grown on a single-crystalline substrate. This discovery is particularly significant in light of the debate about the validity of the polar catastrophe model. In our work, amorphous Al₂O₃ layers were grown on (001) SrTiO₃ single crystals and their morphology, structure, chemistry and electronic properties were studied. Here we focus on a spectroscopic study of the relative band offsets at the amorphous-crystalline oxide interface. Our results provide a quantitative picture of the interface band structure and complement the existing understanding of this 2DEG system. The interface barriers for electrons and holes suggest the potential for Al₂O₃ as a gate insulator for future oxide electronic devices.