We present AlGaN/GaN-based FETs on Si(001) grown by metalorganic vapor phase epitaxy (MOVPE). The influence of the substrate off-orientation on the crystallographic quality is investigated by spatially resolved electron backscatter diffraction. A stringent correlation of the surface morphology of GaN layers grown on differently misoriented Si(001) with two different in-plane alignments of adjacent GaN crystallites is observed. On a 2.5 mu m thick single-crystalline and crack-free GaN-based buffer layer structure, an AlGaN/ GaN FET heterostructure was realized. A drain-source current of 245 mA/mm with a transconductance of 90 mS/mm was achieved. (c) 2007 Elsevier B.V. All rights reserved.