We have studied the process of AlN nucleation on silicon by metal-organic chemical vapor phase deposition. We have shown that for our reactor, which incorporates a chlorine-based chamber clean, we require similar growth conditions to those shown to be optimum by molecular beam epitaxy, that is to say a small amount of NH3 followed by tri-methyl aluminum (TMAl). When TMAl was introduced first, the resulting layers were low quality and cracked. Furthermore, we have shown that for the highest quality layers, with longer TMAl injection, we have an increased density of “inverted pyramid” defects in the layer which can impact electrical device performance. As we have shown that wafer bow becomes increasingly concave with reduced crystalline quality of the GaN layers, a compromise should be achieved between layer quality and morphology to produce wafers which can be processed into large area, high power transistors. We have been able to produce wafers with a low vertical leakage current density <,100 nA mm?2 and high breakdown voltage >,900 V for test structures up to 12 mm2, with a total nitride structure of 3.6 ?m on silicon, resulting in a bow less than <,50 ?m on the 200 mm wafer. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim