Photoemission oscillation from GaAs(001) surfaces illuminated by a deuterium lamp is studied for a highly As‐rich 2×4‐&ggr; phase during molecular beam epitaxy. The 2×4‐&ggr; phase shows higher oscillation amplitude than the As‐poorer 2×4‐&agr; phase. Oscillation of 2×4‐&ggr; occurs as a result of two‐dimensional nucleation, which is confirmed by the suppression of oscillation on highly misoriented GaAs(001) surfaces. Furthermore, the oscillation has its maxima at nearly half‐monolayer growth, which correspond to maximum step‐edge density. For this particular 2×4‐&ggr; phase, this implies that the surface with a higher step‐edge density emits more photoelectron and has a lower ionization energy threshold.