Extracting the trap distribution in charge trapping layers of charge trap flash memory devices, an optical C-V method (OCVM) is proposed. Applying photons with λ=532nm to the oxide-nitride-oxide layer with 50∕60∕23Å in metal-oxide-nitride-oxide-semiconductor charge trap flash devices, the trap density in the charge trapping nitride layer is extracted to be 1.16×1018–1.67×1019cm−3eV−1 over the energy EC−Et=1.36–1.64eV. Combining sub-band-gap photons in C-V characterization, the OCVM method is free from the thermal and electrical stresses which are inherent in conventional characterization methods even though they are critical error factors for accurate characterization of charge trapped flash memory devices.