The role of As-4 molecules in Ga diffusion on the GaAs(001)-(2X4) reconstructed surface has been studied using a combined molecular beam epitaxy and scanning tunneling microscopy multichamber facility. We deposited 10% of a plane of Ga atoms onto an otherwise pristine surface, while exposed to two separate As-4 beam equivalent pressures of 10(-5) and 10(-6) Torr. The higher As-4 flux resulted in the production of fewer and larger islands, indicating that increasing the As-4 flux increases the total interrogation area available to the Ga atoms before forming islands.