an array of stacks containing a semiconductor fins and an oxygen - impermeable cap is formed on a semiconductor substrate with a substantially uniform areal density . oxygen - impermeable spacers are formed around each stack , and the semiconductor substrate is etched to vertically extend trenches . semiconductor sidewalls are physically exposed from underneath the oxygen - impermeable spacers . the oxygen - impermeable spacers are removed in regions in which semiconductor fins are not needed . a dielectric oxide material is deposited to fill the trenches . oxidation is performed to convert a top portion of the semiconductor substrate and semiconductor fins not protected by oxygen - impermeable spacers into dielectric material portions . upon removal of the oxygen - impermeable caps and remaining oxygen - impermeable spacers , an array including semiconductor fins and dielectric fins is provided . the dielectric fins alleviate variations in the local density of protruding structures , thereby reducing topographical variations in the height of gate level structures to be subsequently formed .