Electroreflectance was employed to study the electric-field effect on the interband transitions of InAs quantum dots embedded in an In0.16Ga0.84As matrix. The electric field caused an asymmetric quantum-confined Stark shift, which revealed a nonzero built-in dipole moment in the quantum dots. We found the ground-state and excited-state dipole moments to be in the same direction. The electron wave functions are distributed near the base of the quantum dot, with their centers located below the hole wave functions. We also observed a symmetric Stark shift in the wetting-layer transitions. This implies that the wetting-layer potential is symmetric, despite its being capped with quantum dots.