A method of fabricating a trench device includes forming a first trench and forming a hardmask layer on sidewalls of the trench. A second trench may be etched narrower than the first trench, into the bottom of the first trench. A dielectric material may be grown to substantially fill the second trench, using a reaction process to which the hardmask material is substantially inert. The growing action also grows tapered portions of the dielectric material upwardly under part of the hardmask. A conductive layer may be formed over said dielectric material. The dielectric material in the second trench, in combination with the tapered portions which extend upward from the dielectric material may provide smooth gradation of voltage differences within the semiconductor material. The gradation may be caused by potential differences between the gate and various portions of the semiconductor material.