GaN films were grown on c-Al2O3 substrates with the insertion of AlxGa1-xN (0.5,less than or equal toxless than or equal to1.0)/GaN short period strained-layer superlattices (SPSLSs) at elevated temperatures. It appears that the insertion of an AlxGa1-xN (0.5 less than or equal to x less than or equal to 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 AlxGa1-xN (0.5less than or equal toxless than or equal to1.0)/GaN intermediate SPSLSs on blocking threading dislocation (TD) propagation in GaN films. The presence of intermediate AlxGa1-xN (0.5 less than or equal to x less than or equal to 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. (C) 2003 Elsevier B.V. All rights reserved.