We report on the first use of fiber optic low-coherence interferometry (FOLCI) for non-invasive characterization of semiconductors. The FOLCI sensor system uses an edge-emitting light emitting diode (LED) operating at 1.55 μm as the source for a fiber optic Michelson interferometer. This system has been used to measure silicon wafer thickness and sensor-wafer separation to an accuracy of ±1.5 μm. In these measurements, the sensor head is positioned a centimeter away from the wafer under test. © 1994.