Thermal stresses in chemical vapor deposited (CVD) vitreous silicate and phosphosilicate glass (PSG) films on Si substrates are measuredinsitufrom room temperature (RT) to 900 °C. As‐deposited films grown at one atmospheric (APCVD) and lower pressures (LPCVD) are found to be inherently under a tensile and compressive stress at RT, respectively. On heating to 500 °C, the tensile component of the stress develops in both CVD films. Tensile stress increases with time at a given temperature. In the range 500–900 °C, the tensile component is reduced with temperature and time. During the cooling process from a temperature between 700 and 900 °C, the stress component of APCVD and LPCVD films changes from tension to compression. With APCVD film, the temperature dependence of the stress in the range RT–500 °C can be represented as a function of phosphorous concentration in mol % P2O5. Temperature and time dependence, and thermal hysteresis are attributable to water content, sintering, and viscoelastic properties of CVD film. These are explained from the viewpoint of glass annealing and softening temperature points.