Abstract: An electrostatic chuck for semiconductor wafers (10) uses at least three electrodes (12, 13, 14). Two electrodes (13, 14) defining a substantially planar surface and embedded in a thin dielectric film (11), are respectively excited by a low-frequency A.C. supply (15, 16, 17, 18, 23) to produce sinewave fields of controlled amplitude and phase, provided a low resultant voltage on the wafer surface. A third electrode (12) acts as a shield electrode or as a reference point for the other two electrodes (13, 14). In addition, by controlled rates of voltage application and removal, low voltage gradients are obtained on the wafer (10); and no retentive forces exist in the dielectric medium (11). A low A.C. amplitude excitation of the chuck enables capacitive current sensing of the relative positions of the wafer (10) and the dielectric film (11), enabling simple control of voltage application to the two electrodes (13, 14).