A method forms first and second sets of fins. The first set includes a first stack of layer pairs where each layer pair contains a layer of Si having a first thickness and a layer of SiGe having a second thickness. The second set of fins includes a second stack of layer pairs where at least one layer pair contains a layer of Si having the first thickness and a layer of SiGe having a third thickness greater than the second thickness. The method further includes removing the layers of SiGe from the first stack leaving first stacked Si nanowires spaced apart by a first distance and from the second stack leaving second stacked Si nanowires spaced apart by a second distance corresponding to the third thickness. The method further includes forming a first dielectric layer on the first nanowires and a second, thicker dielectric layer on the second nanowires.