A technique is described for performing MOS capacitance-voltage (CV) measurements on thin Si films on insulating substrates. Such measurements are complicated by the lack of a back contact in SOI structures. Design considerations for an MOS capacitor geometry appropriate for this material were made by treating the structure as a distributed RC circuit. Based on these calculations, a structure has been designed and fabricated that permits both high and low frequency CV measurement and analysis. Use is also made of the Si substrate wafer as a back gate both to provide a back channel for front-gate CV measurements and to characterize the back interface. CV measurements and interface state calculations are presented and compared for SIMOX and laser-recrystallized materials. The experimental results are compared with those of numerical solutions to Poisson's equation.