GaN has been grown on Si(110) substrates by metalorganic vapor phase epitaxy using a low-temperature AlN nucleation layer. The atomic arrangement at the AlN/substrate interface has been investigated by high-resolution transmission electron microscopy. Lattice images of the AlN/Si interface taken along the < 11 (2) over bar >(AlN) // < 1 (1) over bar0 >(Si) and < 1 (1) over bar 00 >(AlN) // < 001 >(Si) projections show an abrupt crystalline interface. A highly coherent epitaxial relationship between < 1 (1) over bar 00 >(AlN) and < 001 >(Si) planes is observed. The atomic bonding configuration at the AlN/Si interface is analyzed taking into consideration the chemical coordination, lattice mismatch, and net charge balance. A structure model of the bonding at the interface is presented. (C) 2008 The Japan Society of Applied Physics.