The microstructural properties of an aluminum nitride (AlN) layer grown on a silicon (Si(110)) substrate were studied in detail using transmission electron microscope techniques to determine atomic structure and dislocation behavior. AlN islands elongated along the [11 (2) over bar0](AlN)//[(1) over bar 10] Si direction were observed at the initial growth stage on the Si(110) substrate. The threading dislocations with a Burgers vector vertical to the interface, most probably b(e) = [0001] of the wurtzite structure, were frequently observed in the AlN thin film. Due to anisotropic biaxial strain distributions, two different atomic structure behaviors were observed along the two in-plane directions; a coherent interfacewas observed along the [11 (2) over bar0](AlN)//[(1) over bar 10] Si direction and a semicoherent interface, including periodic extra-half planes, was observed along the [(1) over bar 100](AlN)//[001] Si direction. The extra-half planes were observed at approximately two monolayers above the interface, and not at the exact interface. (C) 2015 Elsevier B.V. All rights reserved.