Correlations between midgap interface state density (Dit) and thickness‐averaged stress in thermally grown SiO2thin films have been investigated by infrared spectroscopy, an optical beam deflection technique, and capacitance‐voltage measurements. We find no correlations betweenDitand either (i) the maximum stress in the Si or SiO2at the Si/SiO2interface or (ii) the stress gradient in the SiO2film. By direct measurements of the strain‐induced bending of the Si wafer, and by calculating the microscopic strain from the SiOSi bond‐stretching vibrational frequency, we have established linear relationships betweenDitand the thickness‐averaged stress and strain in the oxide.