Photoluminescence studies on AlGaAs/GaAs heterostructures grown by molecular beam epitaxy were carried out to investigate the sub-band properties at the heterointerface. A peak at 1.505 eV associated with the presence of a two-dimensional electron gas layer formed by confined carriers near the heterointerface was observed at low temperature. As the thickness of the spacer layer increased, the photoluminescence intensity and the carrier concentration of the 1.505 eV band decreased with similar slopes, indicating that the emission intensity is closely related to the carrier confinement at the heterointerface. The emission intensity increased as the thickness of the cap layer decreased, and as the carrier concentration increased.