We report on the formation of a BiAg2/Ag/Si(1 1 1) trilayer system which exhibits a giant Rashba spin-splitting of its surface-localized states and is grown on a semiconducting substrate. Angle-resolved photoelectron spectroscopy (ARPES) results reveal the strong interplay of its spin-orbit (SO) splitting and quantum confinement giving rise to a complex gap structure. We suggest that the spin polarization of the system near the Fermi energy can be tailored by varying the thickness of the Ag thin film. Therefore, interesting transport properties are expected which might be useful in the emerging field of spintronics. (C) 2008 Elsevier B.V. All rights reserved.