We have investigated the electronic structure of the Ca/Si(111)-(2×1) surface using angle-resolved photoelectron spectroscopy. Two semiconducting surface states were clearly observed in the bulk band gap, and one was found in a pocket of the bulk band projection. Qualitatively, the dispersions of the two surface states observed in the band gap agree well with theoretical dispersions for a clean Si(111)-(2×1) surface with the Seiwatz structure. Taking this result into account, we conclude that the two surface states in the band gap originate from orbitals of Si atoms that form a Seiwatz structure, and that two electrons are donated from Ca to Si per (2×1) unit cell. This conclusion supports the structure of the Ca/Si(111)-(2×1) surface proposed in the literature.