Closed form solution of nonlinear 2-DEG concentration formula is proposed. This allows us to model continuous 2-DEG charge concentration as the function of gate voltage covering subthreshold region of the I-V curves. Comparisons of the Ids-Vgs characteristics and transconductance with the measured data were performed to show the accuracy of the proposed model. This way we have completely closed form I-V characteristics in subthreshold, triode and saturation region incorporating accurate charge control mechanism for HEMTs.