Atomically flat nanofilms were formed during growth of Ga on a Si(111) surface using an In surfactant above the melting point of Ga (and In–Ga eutectic) throughout Ga coverages of 0.17 to 5 monolayers (0.17≤Θ _Ga ≤5) . Unique superstructures such as a quasisquare-lattice (QS) structure at Θ _Ga =3 to 4 and a 5×5 structure at Θ _Ga =5 appeared as Θ _Ga increased. The QS structure had Ga dimer layers similar to the square lattices of an alpha-Ga(100) plane but also maintained the 1×1 structure of Si(111). As dimer layers transformed into a monoatomic layer, QS transformed into a 5×5 structure that no longer has square features.