We report vertically-aligned InAs islands separated by GaAs barriers thin enough for electronic coupling. Thinner barriers reduced the InAs critical-thickness for island formation. Transmission electron microscopy revealed well-aligned islands with all detected islands in complete stacks. Atomic force microscopy showed the top islands of uncapped stacks are fully formed. The photoluminescence peak was sharper and shifted to lower energy compared to a single-layer growth. We attribute this shift to island-to-island electronic coupling and to the smaller compressive strain in the center of the composite structure.