The kink effect in poly-Si TFTs (thin-film transistors) is evaluated by using a novel method based on kink current and hot carrier light emission measurements. It is revealed by examining the influence of the hydrogenation treatment on the kink current and measuring the temperature dependence of the kink current that the kink effect is significantly influenced by the grain boundary traps. Furthermore, it is found from the hot carrier light emission measurement that the energy distribution of hot carriers is not described by the Maxwell-Boltzmann distribution. The comparison between the kink current and the emitted light intensity suggests that both kink current and light emission basically originated from the hot carriers although the kink current characteristics are not always completely correlated with the light emission properties.<<ETX>>