High-temperature lasing characteristics of randomly assembled ZnO nanowires at ultraviolet wavelength are investigated. Lasing emission was observed from the randomly assembled ZnO nanowires for temperature up to 500 K. The corresponding lasing mechanism is attributed to the coherent random lasing action via the formation of closed-loop cavity modes. Furthermore, ridge waveguide lasers using the randomly assembled ZnO nanowires as the active medium were fabricated. It is found that the width of the ridge waveguides restricted the size of the closed-loop cavity modes such that the corresponding characteristic temperature can be increased by 10 K.