Kink effect is analyzed in AlGaN/GaN devices primarily. A semiempirical model is given by analyzing the kink effect on AlGaN/GaN high electron mobility transistor and by considering the relationship between Vds,kink and gate voltage. Due to a little error between simulation results and measured data, this model can be used to identify the occurrence of kink effect and change in drain current. The analyses of experimental results and model simulation lead to a conclusion that impact ionization plays an important role in generating kink effect.