A pair of identical humidity sensors (S1) and (S2) are in the same environment, so that they identically react to humidity effects; a sensing circuit includes an operational amplifier (10), its input (15) receiving from the first sensor (Si) a signal changing with humidity according to a logarithmic law, while the second sensor (S2), inserted in the amplifier feedback, reacts to humidity changes in the same way as the first sensor (Si) and consistently modifies the gain. The output signal (V.sub.0) is compensated, and has a substantially linear progression with humidity.