As-rich (2 × 2) surface reconstruction on GaAs(111)A

► We studied the structure and formation processes of the As-rich (2×2) reconstruction of GaAs(111)A. ► The As-rich (2×2) surface consists of As trimers at a fourfold atop site with the rest-site As atom. ► The As-rich (2×2) surface is formed only when the Ga-rich (2×2) surface covered with amorphous As layers was annealed. ► The Ga-rich phase is formed by heating the As-rich phase, but the reverse change hardly occurs.