An extremely thin (~0.4 nm) silicon-nitride layer has been deposited on thermally grown SiO2 by an atomic-layer-deposition (ALD) technique. The boron penetration through the stacked gate dielectrics has dramatically been suppressed, and the reliability has been significantly improved, as confirmed by capacitance–voltage, gate-current–gate-voltage, and time-dependent dielectricbreakdown characteristics. The ALD technique allows us to fabricate an extremely thin, very uniform silicon-nitride layer with atomic-scale control.