The moisture resistance of borophosphosilicate glass (BPSG) films annealed at 900 degrees C was studied. The investigation focused on phosphorus leaching from, and water penetration into, films during exposure to a saturated water vapor at 120 degrees C. Phosphorus leaching was measured using x-ray fluorescence spectroscopy and water penetration was measured using secondary ion mass spectroscopy. Water desorption from films after exposure to the water vapor was also measured using thermal desorption spectroscopy. These studies showed that phosphorus in films with a phosphorus concentration exceeding 9 weight percent (w/o) P leached from films during exposure to water vapor, but phosphorus in films with 9 w/o P or less showed scarcely any leaching, regardless of the boron concentration. In films with a phosphorus concentration of 9 w/o P or less, phosphorus suppressed, and boron enhanced, water penetration into the films, but boron had less of an effect with increased phosphorus concentration. A thermal desorption spectroscopy study showed that phosphorus decreases, and boron increases, the number of molecular water absorption sites, apparently the change in the number of water absorption sites changes the degree of water penetration into films. Thus, BPSG films with a higher phosphorus concentration not exceeding 9 w/o P have higher moisture resistance, because films show lower water penetration and scarcely any phosphorus leaching.