a b s t r a c t Complex investigations of the photoconductivity and photoinduced absorption together with the piezoelectric features were performed for the AgGaGeS 4 semiconducting single crystals under the influence of 3.5 ms CO 2 (80 mJ) pulsed laser emitting at 10.6 mm. These crystals are transparent in the wide spectral range 0.4–17 mm, which allows operating due to their properties in the spectral range covering the excitation of the phonons and electron subsystem. The piezoelectric properties show substantial increment during illumination by microsecond CO 2 laser and irreversible relaxation after swathing off the laser excitation. The temperature dependent studies of absorption and photoconduc-tivity confirm the main role of intrinsic defects forming the tails of electronic states below the bottom of conduction band gap. Principal role of IR-induced electron–phonon interactions in the observed changes of the piezoelectricity is demonstrated.