We present impedance spectroscopic analyses made on forward biased minority carrier type metal oxide semiconductor tunnel diodes (MOSTD). Bias dependence of the spectra, i.e. the real and imaginary parts and the Cole-Cole plots, shows the transition of characteristic minority carrier dynamics. At moderate bias levels, interface recombination dominates and the spectra follow the Debye type model with a single time constant determined primarily by the tunneling resistance and by the oxide capacitance. At higher bias levels, a high level of minority carrier injection leads to conductivity modulation in the bulk and the spectra deviate significantly from the prototype model as indicated by an anomalous inductive reactance. The results point to the important role of interfacial ultrathin oxides, i.e. increasing the minority carrier injection ratio, in Schottky diodes.