Infrared spectroscopy is a well-known powerful tool for characterizing the semiconductor thin films. First, we review description of thin films in terms of multiple reflection and transfer matrix. We apply this technique to ferroelectric thin films to obtain information which is important as a feedback for their preparation. We measured the transmittance and reflectance spectra of several perovskite materials and demonstrated potential of this technique. These measurements enable much more direct observation of the soft mode temperature dependence than other techniques as specular reflectance of bulk samples.