We have developed a novel system to obtain a photoluminescence (PL) image with a resolution in a range of sub-mum at 15 K. At a line-shaped surface defect in a 4H-SiC homoepitaxial layer, a PL image of an emission ascribed to excitons bound to neutral nitrogen atoms showed a dark line, indicating that a non-radiative recombination dominates the excitonic emission at the surface defect. The spatial distribution of cubic and hexagonal phases of GaN grown on sapphire by MBE was discriminated with a resolution of 0.4 mum. The microscopic PL imaging is promising for characterization of distributions of polytypism, defects, and impurities in sub-mum scale for SiC and GaN.