In this paper, a novel eight-parameter empirical nonlinear current-voltage (I-V) model for gallium nitride (GaN) high electron mobility transistors (HEMTs) is presented. A hyperbolic sine function is introduced in this model to describe the transfer characteristics between drain-source current, I-ds, and gate-source voltage, V-gs. The self-heating and trapping effects have been considered and incorporated into the proposed model through expansion parameters. The proposed model has been verified on four different types of GaN HEMTs with good agreements between the simulated curves and the measured data. Comparison between the proposed model and other traditional non-square-law models indicates a significant accuracy improvement especially in linear region by the proposed model. This simple but accurate empirical I-V model can be easily implemented for computer aided circuit design and simulation with GaN HEMTs.