The electrical and optoelectronic performance of semiconductor devices are mainly affected by the presence of defects or crystal imperfections in the semiconductor. Oxygen vacancies are one of the most common defects and are known to serve as electron trap sites whose energy levels are below the conduction band (CB) edge for metal oxide semiconductors, including β-Ga₂O₃. In this study, the effects of plasma nitridation (PN) on polycrystalline β-Ga₂O₃ thin films are discussed. In detail, the electrical and optical properties of polycrystalline β-Ga₂O₃ thin films are compared at different PN treatment times. The results show that PN treatment on polycrystalline β-Ga₂O₃ thin films effectively diminish the electron trap sites. This PN treatment technology could improve the device performance of both electronics and optoelectronics.