We report on the preparation and superconductivity of metastable -Ga islands on Si (111) substrate. The Ga grows in a typical
Volmer-Weber mode at a low temperature of 110 K, resulting in formation of Ga nanoislands at various sizes with the identical
-phase. In-situ low temperature scanning tunneling spectra reveal quantized electronic states in ultrathin Ga islands. It is
found that both the lateral size and thickness of the Ga islands strongly suppress the superconductivity. Due to substantial surface
energy contribution, the transition temperature Tc scales inversely with the island thickness and the minimum thickness for
the occurrence of superconductivity is calculated to be two monolayers.