The SiOH concentration profiles as a function of depth within SiO2 films deposited from SiH4, O2, and Ar containing plasmas were measured using real-time attenuated total reflection Fourier transform infrared spectroscopy. The effective thickness approximation in conjunction with mathematical deconvolution of the temporal evolution of the spatially averaged SiOH concentration during deposition allowed the conversion of integrated SiOH absorbance to local SiOH concentration as a function of distance normal to the substrate surface. Thus, depth profiling of SiOH species in growing SiO2 films was realized. As an example, SiOH concentration profiles in SiO2 deposited on Si substrates cleaned with H2 plasma was studied as a function of SiH4-to-O2 gas flow rate ratio. For the depositions performed after H2 plasma cleaning, the local concentration profiles revealed strong evidence of high SiOH density at the SiO2-Si interface. This method can be applied to measuring concentration depth profiles of Si-H, Si-F, or any other infrared active species in plasma-deposited films in real time.