Capacitance-voltage (C-V) traces in n-type-(Bi1-xSbx)(2)Te-3/oxide/metal capacitor structures using an AC capacitance bridge are investigated. By tuning the top gate voltage (V-tg) from positive to negative values, the system at the interface is tuned from accumulation, via depletion into inversion. The results show the typical low-frequency and high frequency C-V traces, depending on measuring frequency, temperature, and illumination intensity and reflecting their sensitive dependence on recombination/generation rates. Superimposed a strong hysteresis under inversion is also observed which is ascribed to the presence of conventional localized surface states (LSS) which coexist with topological surface states (TSS).