A method of forming an isolated structure of sufficient size to permit the fabrication of an active device thereon is comprised of the steps of depositing a gate oxide layer on a substrate. Material, such as a polysilicon layer and a nitride layer, is deposited on the gate oxide layer to protect the gate oxide layer. An active area is defined, typically by patterning a layer of photoresist. The protective material, the layer of oxide, and finally the substrate are etched to form a trench around the active area. Spacers are formed on the sides of the active area. The substrate is etched to deepen the trench around the active area to a point below the spacers. The substrate is oxidized at the bottom of the trench and horizontally under the active area to at least partially isolate the active area from the substrate. Oxide spacers are formed on the sides of the active area to fill exposed curved oxide regions and the remainder of the trench may be filled with an oxide.