The electrical properties of m.i.s. structures based on InP and Langmuir films have been investigated. A strongly inverted low-frequency-type C/V response occurs at about 30 Hz. Surface-state distributions have been evaluated by using both quasistatic and conductance techniques. Effective surface-state densities are found to be ~3 × 1011cm−2 eV−1 over a large fraction of the band gap.