AlN/W superlattices with bilayer periods of 3.5-7 mn were grown on MgO (001) by magnetron sputtering. For AlN thicknesses l(AlN)less than or equal to1.5nm, a cubic phase of AlN was observed using high-resolution cross-sectional transmission electron microscopy and x-ray diffraction (XRD). Pole-figure XRD scans showed a reflection that matched the theoretically predicted interplanar spacing of zinc-blende, phase (Zb-AlN), and that could not be explained by either the wurtzite or rocksalt structures. The stabilization of zb-AlN is explained as a result of good interfacial matching between W(100) and zb-AlN(011). When l(AlN) was increased above 1.5 nm, XRD scans showed a rapid decrease in satellite peak intensities, indicating a degradation of the layered structure, and the appearance of a wurtzite structure.