A method of a forming semiconductor fin structures that includes forming a plurality of fin structures with a first etch to a first depth in a substrate. The plurality of fin structures have a first width to the first depth. A spacer is formed on sidewalls of the plurality of fin structures. A second etch step can then extend the plurality of fin structures to a second depth with a second etch. The plurality of fin structures have a second width greater than the first width at the second depth portion. At least a portion of the trench separating adjacent fin structures may then be filled with a dielectric formed by an oxidation process. The portion of the fin structures extending above the dielectric fill is the active region of the fin structures which has a uniform height for all of the fin structure in the plurality of fin structures.