The piezoelectric response of a sample (3) is measured by applying a scanning probe microscope, whose probe (2) is in contact with the sample (3). The probe is mounted to a cantilever (1) and an actuator (5) is driven by a feedback loop (7, 11, 12, 4) to oscillate at a resonance frequency f. An AC voltage with principally the same frequency f but with a phase (with respect to the oscillation) and/or amplitude varying periodically with a frequency fmod is applied to the probe for generating a piezoelectric response of the sample (3). A lock-in detector (20) measures the spectral components at the frequency fmod of the control signals (K, f) of the feedback loop. These components describe the piezoelectric response and can be recorded as output signals of the device. The method allows a reliable operation of the detector oscillator resonator (1) at its resonance frequency and provides a high sensitivity.