A method to drastically reduce dislocation density in a GaN film grown on sapphire substrate is newly developed. In this method, a very thin SixN1-x was deposited on the sapphire substrate at low temperature before growing conventional low-temperature GaN buffer layer. By transmission electron microscope (TEM), the density of threading dislocation originating from the interface between a sapphire substrate and GaN layer decreases to be almost invisible in the observed area from 7 x 10(8/)cm(2) in the conventional method. Atomic force microscopy of a deposited thin SiN indicates that there exists nanometer-sized holes in a thin SiN layer, which probably enhance lateral growth and then decrease the dislocation density. The electrical properties were investigated with respect to the SiN deposition time. With the increase of SiN deposition time up to 125 s, the mobility increases and the carrier density decreases. However. if the SiN deposition time is further increased, the mobility decreases and the carrier density increases.