The growth of hexagonal Gd disilicide nanowires on Si(100) is studied by scanning tunneling microscopy. Gd disilicide nanowires are grown on Si(100) by submonolayer Gd deposition on the substrate at 600 degreesC. The formation of nanowires is shown to be due to anisotropic lattice mismatches between hexagonal Gd disilicide and Si. The nanowires have widths of several nanometers and lengths up to micrometer length scales. The top of the nanowires has a c(2x2) structure, indicating that the crystalline structure is Si-deficient Gd disilicide. The nanowires were shown to have metallic properties using scanning tunneling spectroscopy. (C) 2003 American Institute of Physics.