We determined the optical and electrical characteristics of GaN-based, ultraviolet micro light emitting diodes (microLEDs). Such microLEDs are essential to next-generation high-resolution micro-displays. Square-shaped microLEDs of different sizes (side lengths: 5-50 μm) were designed. The peak emission wavelength of these devices shifted <0.15 nm during the current injection. The 50 μm device had a 3.8 times greater relative illumination intensity than did the 5 μm device, suggesting a degradation in quantum efficiency in small devices. Measurements of temperature-dependent reverse leakage current indicated (1) thermal activation from deep centers and (2) a high percentage of components with surface recombination current in the small devices.