The linear optical response of semiconductor microcavities with embedded quantum wells has been investigated by ellipsometry and reflectivity in the range of the stop-hand including the resonator mode. The experimental results are compared with calculated spectra using the transfer-matrix technique. The comparison confirms the effective metal-like behaviour of this non-absorptive system as well as the sensitivity of the response against small variations of the transition energy and position of the quantum wells. The dielectric function of simple Bragg-reflectors and complete resonator structures are presented followed by the discussion of the observed mode splitting of the reflectivity spectra.