We present a theoretical model beyond the small-signal. approximation for Schottky junction differential admittance for the general case of an arbitrary temperature, measurement signal frequency and amplitude, and doping occupation number. Shockley-Read-Hall statistics, an equilibrium nondegenerate free carrier distribution, a uniform impurity concentration, and a negligible minority carrier concentration are assumed. To show the influence of the carrier freeze-out effects we calculate the frequency dependence of a Schottky junction capacitance for the case of N-doped SiC. We compare results of calculations using the new model and models based on the truncated space charge approximation and small-signal approximation.