In situ growth interrupts were executed during the growth of 8 degrees off-cut 4H-SiC epitaxial layers to determine the dependence of the efficiency for converting basal plane dislocations (BPDs) to threading edge dislocations (TEDs) on the interrupt temperature. Three samples were grown with 15 min growth interrupts executed near the middle of a 30-40 mu m thick, n-type doped layer at 1400, 1500, and 1580 degrees C. Ultraviolet photoluminescence (UVPL) mapping of these layers reveals the BPDs and permits the observation of how these defects extend into and through the epilayer. From the lateral length of the BPDs in the UVPL wafer map, it was determined whether or not the BPD converted into a TED at the growth interrupt interface. The percentage of BPDs that converted for the 1400, 1500, and 1580 degrees C interrupts were 20%, 28%, and 51%, respectively. The proposed cause for the higher conversion rate at the interrupt temperature of 1580 degrees C is the higher etching rate that occurs at this temperature, and it is presumed that there is an enhanced etch rate where the BPD intersects the surface which will result in etch pit decorations. It was also observed that no new in-grown stacking faults formed at the growth interrupt interface, as has been observed for ex situ growth interrupts. (C) 2008 American Vacuum Society.