The electro-optic properties of self-organizedIn0.4Ga0.6As/GaAsquantum dots have been studied experimentally. Single-mode ridge waveguide structures were grown by molecular beam epitaxy with self-organizedIn0.4Ga0.6As/GaAsquantum dots in the guiding region. The measured linear and quadratic electro-optic coefficients are2.58×10−11m/V and6.25×10−17 m2/V2,respectively, which are much higher than those obtained for bulk GaAs or quantum well structures. The measured transmission characteristics indicate that low-voltage amplitude modulators can be realized with quantum dot active regions. ©1998 American Institute of Physics.