The roughness of the Si(100)/SiO2interface is measured using both surface second harmonic generation (SSHG) and x-ray scattering. A comparison between these techniques shows a clear correlation for typical industrial oxides, despite the techniques being sensitive to differing regions of the roughness spectrum. The SSHG measurements are made using∼10 fs pulses centered at 850 nm and at 80 MHz repetition rate. The short pulses produce a similar signal to noise ratio as earlier measurements, but use much lower average power, thus avoiding possible artifacts such as sample heating. ©1997 American Institute of Physics.