A method for measuring a surface potential of a portion of material (P), wherein an electrically conductive detection tip is placed above a surface (S) of said portion of material, with a first piezoelectric actuator arranged to control a mean distance of the detection tip above said surface of the portion of material, and a second piezoelectric actuator arranged to control a mechanical oscillation of said detection tip above said surface of the portion of material as a function of a voltage existing between two control electrodes of said second piezoelectric actuator, said method comprising the following steps: - applying a measurement voltage (V M ) between the detection tip and the portion of material, said measurement voltage comprising a DC component (V M ) and an AC component (V M (ω E )) having a selected angular frequency of excitation (ω E ); - simultaneously detecting variations in the instant height (h) of the detection tip ; - measuring an amplitude of a component (h(ω E )) of said variations in the instant height of the detection tip, for said angular frequency of excitation; and - adjusting a value of the DC component (V M ) of the measurement voltage so as to reduce or cancel the amplitude of the component (h(ω E )) of the variations in the instant height of the detection tip for the angular frequency of excitation, the adjusted value of said DC component of the measurement voltage constituting a result of the measurement of the surface potential of the portion of material (P); the method being characterized in that , while the variations in the instant height (h) of the detection tip are being detected: - the two driving electrodes of the second piezoelectric actuator are electrically connected to two respective reference terminals ; and - a control voltage is applied between the two driving electrodes of the second piezoelectric actuator through the two reference terminals , said control voltage having a zero AC component amplitude for the angular frequency of excitation (ω E ). - applying a measurement voltage (V M ) between the detection tip and the portion of material, said measurement voltage comprising a DC component (V M ) and an AC component (V M (ω E )) having a selected angular frequency of excitation (ω E ); - simultaneously detecting variations in the instant height (h) of the detection tip ; - measuring an amplitude of a component (h(ω E )) of said variations in the instant height of the detection tip, for said angular frequency of excitation; and - adjusting a value of the DC component (V M ) of the measurement voltage so as to reduce or cancel the amplitude of the component (h(ω E )) of the variations in the instant height of the detection tip for the angular frequency of excitation, the adjusted value of said DC component of the measurement voltage constituting a result of the measurement of the surface potential of the portion of material (P); - the two driving electrodes of the second piezoelectric actuator are electrically connected to two respective reference terminals ; and - a control voltage is applied between the two driving electrodes of the second piezoelectric actuator through the two reference terminals , said control voltage having a zero AC component amplitude for the angular frequency of excitation (ω E ). <EOS>