Low-temperature (LT) GaN layers with a columnar microstructure were grown on InN layers with various thicknesses. Subsequently, thick, hightemperature GaN layers were grown on the columnar LT GaN/InN/sapphire template. The microstructure of the InN interlayer and the LT GaN columnar structure were investigated by transmission electron microscopy. From the X-ray diffraction analysis, it was shown that the InN layer was decomposed at the initial stage of LT GaN growth. The depth profile of Ga and In atoms from the GaN/InN/sapphire structure obtained by secondary ion mass spectrometry showed that the distribution of In atoms was confined only within the columnar LT GaN and InN/GaN layer interface. Wafer bowing was measured by optical methods and a significant reduction in the extent of wafer bowing was observed for the samples with the columnar LT GaN layer compared with the GaN layer grown on conventional LT GaN buffer layers. It is suggested that the epitaxial growth of a columnar LT GaN layer induced by a polycrystalline InN interlayer helped relax the GaN layer strain energy associated with thermal expansion mismatch, resulting in a less bowed GaN epitaxial layer on the sapphire substrate.