The first observation of the resonant Stark tuning of second harmonic generation is reported. Our AlInAs/GaInAs asymmetric coupled-well structures are engineered in such a way that certain intersubband transitions (1 --> 2 and 2 --> 3) exhibit a large Stark shift equal to the potential drop between the centers of the wells. Thus the second-order susceptibility \chi-2-omega(2)\ exhibits a pronounced peak when the bound states are made equally spaced by the application of an electric field and HBAR-omega = DELTA-E12. A peak \chi-2-omega(2)\ = 7.5 X 10(-8) m/V, approximately 200 times the bulk values in InAs and GaAs, has been measured.