A two‐beam laser reflection technique was used to measure SiO2film stress during Si oxidation, i.e.,insituat the growth temperature. Results show a higher compressive intrinsic film stress near the Si–SiO2interface and a lower stress in the bulk of the SiO2film. Thermal stress is also measured by monitoring the SiO2film covered Si substrate curvature changes during temperature excursions. Our new results are in general agreement with previousexsitustress measurements and may indicate that film stress, being highest at the interface, influences the interface reaction in Si oxidation.