Polysilicon/silicon-nitride/thermal-oxide/n-Si (SNOS) and polysilicon/oxide/silicon-nitride/thermal,oxide/n-Si (SONOS) capacitors were fabricated with various nitride thicknesses. It is shown that formation of an oxide layer on the nitride (NOX) reduces current conduction by more than two orders of magnitude at higher fields. Studies of the flat-band voltage shift with injected carrier fluence show opposite flat-band voltage shifts for SNOS (negative) and for SONOS (positive), under positive gate stress. NOX apparently acts as a hole injection barrier.