In this work, we demonstrated the electron/hole injections in the gate of p-GaN/AlGaN/GaN power transistors at forward gate bias by capturing the electroluminescence (EL) emission from the gate region. The EL included both visible and ultraviolet (UV) luminescence. The dynamic switching tests were carried out to investigate the effect of electron and hole injections on device performances. The electron injection and trapping at the forward gate bias caused positive threshold voltage shift, while the injection of holes into the GaN channel induced the emission of the UV light and the resulting leakage current increase in the device.