Field isolation structures and methods of forming field isolation structures are described. In one implementation, the method includes etching a trench within a monocrystalline silicon substrate. The trench has sidewalls and a base, with the base comprising monocrystalline silicon. A dielectric material is formed on the sidewalls of the trench. Epitaxial monocrystalline silicon is grown from the base of the trench and over at least a portion of the dielectric material. An insulating layer is formed over the epitaxial monocrystalline silicon. According to one implementation, the invention includes a field isolation structure formed within a monocrystalline silicon comprising substrate. The field isolation structure includes a trench having sidewalls. A dielectric material is received on the sidewalls within the trench. Monocrystalline silicon is received within the trench between the dielectric material of the sidewalls. An insulating layer is received over the monocrystalline silicon within the trench. Additional implementations are contemplated.