Substrates of GaN over silicon suitable for forming electronics devices such as heterostructure field effect transistors (HFETs), and methods of making the substrates, are disclosed. Voids in a crystalline Al2O3 film on a top surface of a silicon wafer are formed. The top surface of the silicon wafer is along the silicon crystal orientation. A plurality of laminate layers is deposited over the voids and the Al2O3 film. Each laminate layer includes an AlN film and a GaN film. A transistor or other device may be formed in the top GaN film.