Highly efficient electrical spin injection and detection between ferromagnetic electrodes and semiconductors are important technologies for semiconductor-based spintronic devices, such as spin-MOSFETs. In an ideal system, the efficiency of spin injection and detection in a ferromagnetic metal/tunnel barrier/semiconductor junction depends on the spin polarization of the ferromagnetic metal, the spin filtering efficiency of the tunnel barrier, and the conductivity matching condition. However, other complex mechanisms affect spin-dependent transport in real junctions. It has been pointed out that a sequential tunneling process through localized states at an interface of a junction affect an amplitude and a width of Hanle signal so that the calculated spin lifetime are affected by effects of localized states [1-4]. Recently, the effects of these localized states were directly investigated by inelastic electron tunneling spectroscopy (IETS) [5-7]. The purpose of this study is to reveal relationship between the localized states and the spin-dependent transport properties in more detail by means of dependence of the differential conductance and IET signals on the measurement frequency.