Conventional undoped gallium nitride (GaN) surface was treated with trimethylgallium (TMGa) flow for 100 s in the ambient of H2 and low ammonia at 500 °C and 500 Torr followed by thermal annealing at 1050 °C. On the Gallium droplets and GaN nanoislands patterned layer-structured surface, droplet homoepitaxy of thin GaN layers was realized by flowing the surface with TMGa and low ammonia at 1035 °C for 400 s in the ambient of H2. By such an in situ three-step surface modification, the surface stoichiometry (Ga/N) changed from nonstoichiometry (N-rich, 0.92) to close-to-stoichiometry (slightly Ga-rich, 1.04) with very thin nanoislands (20 nm in diameter and 1 nm in height) patterning on the smooth layer-structured surface. Photoluminescence studies show significant reduction of yellow/blue emissions, which suggests improvement of surface/interface qualities of GaN films.