AbstractWe have fabricated a Fabry‐Perot (FP) microcavity in the THz region with a GaP crystal as the cavity layer by using a simple stacking method. We utilized the FP cavity structure as the electro‐optic (EO) material for THz wave detection in the EO sampling of THz time domain spectroscopy. We observed three‐fold enhancement in the THz detection efficiency in the FP cavities as compared to the bare GaP crystal at the frequencies of resonant modes and stopband edges. This enhancement in THz detection efficiency is caused by the incidental THz electric field enhancement effect in the FP cavity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)