ZnO hexagonal prism crystals were synthesized from ZnO powders by microwave heating in a short time (within 20 min) without any metal catalyst or transport agent. Zinc oxide raw materials were made by evaporating from the high-temperature zone in an enclosure atmosphere and crystals were grown on the self-source substrate. The inherent asymmetry in microwave heating provides the temperature gradient for crystal growth. Substrate and temperature distribution in the oven show significant effects on the growth of the ZnO crystal. The morphologies demonstrate that these samples are pure hexagonal prism crystals with maximum 80 μm in diameter and 600 μm in length, which possess a well faceted end and side surface. X-ray diffraction (XRD) reveals that these samples are pure crystals. The photoluminescence (PL) exhibits strong ultraviolet emission at room temperature, indicating potential applications for short-wave light-emitting photonic devices. ZnO hexagonal prism crystals were synthesized from ZnO powders by microwave heating in a short time (within 20 min) without any metal catalyst or transport agent. Zinc oxide raw materials were made by evaporating from the high-temperature zone in an enclosure atmosphere and crystals were grown on the self-source substrate. The inherent asymmetry in microwave heating provides the temperature gradient for crystal growth. Substrate and temperature distribution in the oven show significant effects on the growth of the ZnO crystal. The morphologies demonstrate that these samples are pure hexagonal prism crystals with maximum 80 μm in diameter and 600 μm in length, which possess a well faceted end and side surface. X-ray diffraction (XRD) reveals these these samples are pure crystals. The photoluminescence (PL) exhibits strong ultraviolet emission at room temperature , indicating potential applications for short-wave light-emitting photonic devices.