The barrier properties of silicon nitride films prepared by plasma-enhanced chemical vapor deposition (PECVD) against moisture penetration were studied, with emphasis on the correlation of deposition parameters and moisture permeation rate. The moisture resistance of films have been characterized using infrared spectroscopy and determination of water vapor permeation (WVP) rate. Our results indicate that the gas flux ratio and discharge frequency are the most important factors in controlling the moisture resistance of these films. The best moisture-resistant property in terms of WVP and stability of the film is found in the film deposited in a low frequency (LF) process with lower ratio of silane to ammonia although the general trend is toward decreased WVP with a higher ratio of silane to ammonia in the films deposited freshly by both high and low frequency processes. Too high a ratio of silane to ammonia in LF processes leads to instability of the film after long exposure in a high humidity environment.