Impedance spectroscopy with temperature as a parameter is shown to be sensitive to deep-level states in an n-GaAs Schottky diode. A mathematical model is developed which accounts or the influence of electronic transitions involving deep-level states on the impedance response of the device. Regression of the model to the data is shown to require a weighting strategy that accounts for the variance of the measurements. The parameters obtained are compared to those obtained by deep-level transient spectroscopy and those reported in the literature. Good agreement was seen for the number; concentration, and activation energies of deep-level states, but the reaction cross sections obtained differed from those obtained by deep-level transient spectroscopy by several orders of magnitude. This discrepancy is attributed to the need to refine the process model to account for the influence of recombination pathways on the leakage current observed at low frequencies.