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The surface structure of Si(111) √3×√3-Ag has been analyzed from the X-ray intensity versus energy curves measured both for the integral- and fractional-order spots. A modified trimer model with three Ag atoms in the √3×√3 unit cell is proposed, in which triangles made of Ag atoms are chained in a honeycomb arrangement. The distances between the nearest neighbor Ag atoms are about twice the van der Waals radius. The height of the Ag layer measured from the ideal first Si layer is 2.9±0.1 A. The center of each triangle coincides with the position of the honeycomb protrusion observed by scanning tunneling microscopy.

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