We discuss a new technique for measuring the net carrier concentrations, layer thicknesses, and deep level spectra of epitaxial InP and related compounds used in photonic device applications. The technique involves the formation of an organic‐on‐inorganic (OI) semiconductor contact barrier by vacuum sublimation of the compound: 3, 4, 9, 10‐perylenetetracarboxylic dianhydride onto an inorganic semiconductor wafer. The OI barriers are reproducible from wafer to wafer, and can be as high as &fgr;Bn≊0.55 V over the entire range of InGaAs (P) compounds lattice matched to InP. High voltages (≳100 V in some cases) can be applied to the small area OI devices (as defined by an ohmic contact pad deposited on the organic film), allowing for deep depletion. Thus, high resolution carrier concentration measurements over extensive distances in all three wafer dimensions are obtained. These data are used to derive both the doping levels and layer thickness contours over the crystal surface. Finally, the OI devices can be removed after wafer evaluation, and the wafer can then undergo processing into conventional devices with no apparent degradation of performance when compared with control wafers that have not undergone OI diode evaluation.