We have detected defects micro-pipes and a cluster of impurities in semi-insulating 6H-SiC substrates using long-wavelength infrared thermal imaging camera (IR-camera) with 8 ~ 14 µm in non-destructive and non-contact. Also we have evaluated the thermal influence of defects on the entire substrates from the observation results of scanning laser microscope (SLM) and light scattering tomography (LST). Through the process, it was certificated that the defects in the substrates could be detected with relatively macroscopic scale (8 6 mm2). Moreover, through a temperature profile processing by a 0.1 K thermal resolution, we estimated thermal behavior of the defect areas in the 6H-SiC precisely. The IR-camera is considered as effective technique for evaluating the defects in the intermediate range between micro and macro scale.