Photon emission and the electrical characteristics of a InGaZnO (IGZO) thin-film transistor (TFT) were evaluated to clarify the existence of hot carriers and their effects. The photon emission was observed from the drain edge of the IGZO-TFT and the capacitance–voltage characteristics indicated that a potential barrier was formed at the drain region when the device is driven by high drain voltage of 30 V. Based on these results, the photon emission phenomenon from the IGZO-TFT was induced by hot carriers that should be considered as a significant degradation mode for a high-performance oxide semiconductor device.