A method of operating a gas sensor, in particular to enhance the selectivity of a metal oxide gas sensor , including applying heat by a heater (MHP, 104) to a metal oxide sensing element of a gas sensor , varying the heat applied by said heater (MHP, 104) to said metal oxide sensing element for at least a time interval (Tm), and measuring at least an electrical resistance (R) of said metal oxide sensing element of the gas sensor versus said variation of the heat (I h ) applied to the metal oxide sensing element for a time interval (Tm), comparing said measurement (C) of at least the electrical resistance (R) of said metal oxide sensing element versus said variation of the heat (I h ) applied to the metal oxide sensing element to a set of corresponding reference measurements (P0, P1; SS) associated to a plurality of different target gases (G1...G4), characterized in that said measuring operation includes measuring a further sensor parameter (R D ), proportional to a gas concentration, said further sensor parameter (R D ) being an electrical resistance value of said metal oxide sensing element corresponding to a constant level of heater current (Ih) without modulation, versus the variation of said electrical resistance (R) of said metal oxide sensing element of the gas sensor and said variation of the heat (I h ) applied to the metal oxide sensing element obtaining a trajectory in three dimensions (C) corresponding to the variation of said sensor resistance (R), the variation of said heat (I h ) and the variation of said further sensor parameter (R D ), proportional to a gas concentration, said comparing operation includes comparing said trajectory in three dimensions (C) to a set of reference three-dimensional objects (SS), represented according to the same said three dimensions corresponding to the variation of said sensor resistance (R), said heat (I h ) and said further sensor parameter (R D ), proportional to a gas concentration. applying heat by a heater (MHP, 104) to a metal oxide sensing element of a gas sensor , varying the heat applied by said heater (MHP, 104) to said metal oxide sensing element for at least a time interval (Tm), and measuring at least an electrical resistance (R) of said metal oxide sensing element of the gas sensor versus said variation of the heat (I h ) applied to the metal oxide sensing element for a time interval (Tm), comparing said measurement (C) of at least the electrical resistance (R) of said metal oxide sensing element versus said variation of the heat (I h ) applied to the metal oxide sensing element to a set of corresponding reference measurements (P0, P1; SS) associated to a plurality of different target gases (G1...G4), characterized in that said measuring operation includes measuring a further sensor parameter (R D ), proportional to a gas concentration, said further sensor parameter (R D ) being an electrical resistance value of said metal oxide sensing element corresponding to a constant level of heater current (Ih) without modulation, versus the variation of said electrical resistance (R) of said metal oxide sensing element of the gas sensor and said variation of the heat (I h ) applied to the metal oxide sensing element obtaining a trajectory in three dimensions (C) corresponding to the variation of said sensor resistance (R), the variation of said heat (I h ) and the variation of said further sensor parameter (R D ), proportional to a gas concentration, said comparing operation includes comparing said trajectory in three dimensions (C) to a set of reference three-dimensional objects (SS), represented according to the same said three dimensions corresponding to the variation of said sensor resistance (R), said heat (I h ) and said further sensor parameter (R D ), proportional to a gas concentration. <EOS>