We show experimentally that current-voltage characteristics of double-barrier resonant tunneling devices (DBRTDs) can be modified by internal polarization fields due to the piezoelectric effect induced by external uniaxial stresses. Electric polarization fields, perpendicular to the interfaces, . arise in DBRTDs grown on (001)-oriented substrates under uniaxial, compressive stresses parallel to the (110) or (110) crystal orientations, and in DBRTDs grown on (111)B-oriented substrates under stress parallel to (111) crystal orientation. The voltages at which the resonant tunneling current peaks occur (peak voltages) are sensitive to the polarization fields induced by external stresses. The peak voltages can shift to more positive voltages or more negative voltages depending on the directions of applied stresses. We measured current-vol tage characteristics of AlAs/GaAs/ AlAs double-barrier resonant tunneling structures as a function of external stresses at 77 K. Uniaxial stress was applied parallel to the (110) and the (110) crystal orientations for (001)-oriented DBRTDs, as well as to the (111) orientation for (111)B-oriented DBRTDs. With the substrates grounded in all the measurements, we found that the peak voltages shift to more positive voltages for (001)-oriented DBRTDs under stress along the (110) orientation and for (111)-oriented DBRTDs under the stress along (111) orientation, and to more negative voltages for (001)-oriented devices under stress along the (110) orientation. The results are in agreement with our calculations published in the preceding article, which take into account the piezoelectric effect and band alignment under stress.