Disclosed is a semiconductor fin construction useful in FinFET devices that incorporates an upper region and a lower region with wherein the upper region is formed with substantially vertical sidewalls and the lower region is formed with inclined sidewalls to produce a wider base portion. The disclosed semiconductor fin construction will also typically include a horizontal step region at the interface between the upper region and the lower region. Also disclosed are a series of methods of manufacturing semiconductor devices incorporating semiconductor fins having this dual construction and incorporating various combinations of insulating materials such as silicon dioxide and/or silicon nitride for forming shallow trench isolation (STI) structures between adjacent semiconductor fins.