A semiconductor device includes a semiconductor substrate having a surface, buried isolation regions protruding from the surface of the semiconductor substrate, and a first insulating layer on the surface of the semiconductor substrate between the isolation regions and including a fluorine, nitrogen, and/or heavy hydrogen impurity. A floating electrode is on the first insulating layer, a second insulating layer is on the floating electrode and the isolation regions, and a control gate electrode is on the second insulating layer. Related methods of forming semiconductor devices are also disclosed.