The authors report on the growth of GaN by nitrogen plasma-assisted molecular beam epitaxy (MBE) on a 2 in. Si (111) substrates with a nanothick (similar to 4.8 nm thick) gamma-Al2O3 as a template/buffer. A thin layer of MBE-AlN similar to 40 nm thick was inserted prior to the growth of GaN. High-resolution transmission electron microscopy (HR-TEM) and high-resolution x-ray diffraction studies indicated that both of the nanothick gamma-Al2O3 and AlN are a single crystal. Reflection high-energy electron diffraction, high-resolution x-ray scattering using synchrotron radiation, and cross-sectional HR-TEM measurements indicated an orientation relationship of GaN(0002)parallel to AlN(0002)parallel to gamma-Al2O3(111)parallel to Si(111) and GaN[10-10]parallel to AlN[10-10]parallel to gamma-Al2O3[2-1-1]parallel to Si[2-1-1]. A dislocation density of 5x(10(8)-10(9))/cm(2) in the GaN similar to 0.5 mu m thick was determined using cross-sectional TEM images under weak-beam dark-field conditions. (C) 2008 American Vacuum Society.