GaN films were grown on c-Al 2O 3 substrates with the insertion of Al x Ga 1− x N (0.5⩽ x⩽1.0)/GaN short period strained-layer superlattices (SPSLSs) at elevated temperatures. It appears that the insertion of an Al x Ga 1− x N (0.5⩽ x⩽1.0)/GaN SPSLS having certain thickness and pair combinations is helpful to reduce the etching pit density (EPD) in GaN film for more than one order of magnitude. Cross-sectional transmission electron microscopic (XTEM) observations confirm the efficiency of Al x Ga 1− x N (0.5⩽ x⩽1.0)/GaN intermediate SPSLSs on blocking threading dislocation (TD) propagation in GaN films. The presence of intermediate Al x Ga 1− x N (0.5⩽ x⩽1.0)/GaN SPSLS in a GaN film is believed to encourage TD density reduction in the film through TD annihilation and de-multiplication processes involving interactions between two edge-type TDs.