We grow the Mg0.24Zn0.76O thin film onto a quartz substrate by the radio frequency magnetron sputtering technique. Planar geometry metal-semiconductor-metal structured ultraviolet detectors were fabricated by conventional ultraviolet lithography and wet etching on the Mg0.24Zn0.76O thin films. To improve the performance of the device, three kinds of photodetectors with different electrode width were fabricated, after a series of tests on those device, it is amusing to find an interesting phenomenon, the Mg0.24Zn0.76O photodetectors with different electrode width have a great influence on the performance of the whole device. The Mg0.24Zn0.76O photodetectors that own larger electrode width had a higher responsivity and lower dark current than the photodetectors own littler electrode width. These interesting results are very meaningful for the photodetector industry.