PN junction with p-Si/n-Ga2O3 structure was developed by metal organic chemical vapor deposition (MOCVD) technology on p-type Si (111) substrate. The crystal structure, surface morphology and surface roughness were measured by X-ray diffractometer and atomic force microscope. Then Ti/Au electrodes on these samples were developed by magnet sputtering and evaporation for testing the PN junction characteristics such as I-V curve chart, threshold voltage, on-off current ratio, reverse saturation current, ideal factor, and the barrier height at zero bias voltage. The regulation of PN junction characteristics with growing parameters such as doping concentration and film thickness was studied, and the reasons were given. The crystal quality of β-Ga2O3 thin film and the characteristics of the devices were improved by two-step growing method. A set of PN junction samples were fabricated at three different temperatures when the buffer was developed. Finally, the best conditions of fabricating the PN junction devices was found, and the lattice mismatch and thermal mismatch between Si substrate and β-Ga2O3 thin film were reduced. A high quality n-type β-Ga2O3 thin film with surface roughness of 4.21 nm and a PN junction with low ideal factor of 42.1 was obtained.