A method of forming a semiconductor device includes forming a plurality of trenches extending into a semiconductor substrate from a first surface of the semiconductor substrate. Each of the trenches includes a narrower part in open communication with a wider part that is spaced apart from the first surface by the narrower part. The narrower part of adjacent trenches is laterally separated by a first region of the semiconductor substrate. The wider part of adjacent trenches is laterally separated by a second region of the semiconductor substrate that is narrower than the first region. The method further includes introducing an oxidizing agent into the wider part of the trenches through the narrower part of the trenches to oxidize the second region of the semiconductor substrate between adjacent trenches to form dielectric support structures that support the first region of the semiconductor.