A thick gallium nitride (GaN) film is formed on a LiAlO2 substrate through two stages. First, GaN nanorods are formed on the LiAlO2 substrate through chemical vapor deposition (CVD). Then the thick GaN film is formed through hydride vapor phase epitaxy (HVPE) by using the GaN nanorods as nucleus sites. In this way, a quantum confined stark effect (QCSE) becomes small and a problem of spreading lithium element into gaps in GaN on using the LiAlO2 substrate is mended.