This paper describes the electrical and physical characteristics of ultrathin Jet Vapor Deposited (JVD) Silicon Oxynitride films. Capacitance-Voltage measurements indicate an equivalent oxide thickness (EOT) of less than 2 nm, taking into account the quantum-mechanical correction. These films have leakage currents almost two orders of magnitude lower than thermal oxide of the same equivalent thickness. Measurements on NMOSFETs with 0.15 μm of channel length demonstrate excellent electrical properties, including high drive currents (∼0.5 mA/μm @ Vd=Vg–Vt=l.5 V), low sub-threshold swings (∼72 mV/decade), and high transconductance (∼0.36 mS/μm @ Vd=1.5 V). These films were also analyzed using a variety of physicochemical methods, including Total X-ray Fluorescence (TXRF), Atomic Force Microscopy (AFM), Nuclear Reaction Analysis (NRA), Low Energy (500 eV) Secondary Ion Mass Spectrometry (SIMS), and Transmission Electron Microscopy (TEM). Surface metal concentrations of less than 1011 atoms/cm2 were measured from the TXRF analysis. The microroughness values for these films varied between 0.15 – 0.17 nm as measured by AFM. Low energy (500 eV) SIMS and NRA indicate high [N] near the top as well as throughout the bulk of the film, and a significant amount of [O] near the top of the film. High Resolution TEM pictures show a very uniform film with a physical thickness of 2.8 ± 0.1 nM, which yields an effective dielectric constant of 5.5, consistent with these types of oxynitride films.