Appreciable increases in capacitance have been observed in thin single‐crystal CdS platelets when measured under conditions of dc bias. Data have been obtained in the frequency range 20 cps‐20 Mc/sec. Crystals could be roughly divided into two groups (denoted by I and II). Group I crystals, exhibiting an approximateV2dependence of theI‐Vcharacteristic, showed low‐frequency‐capacitance increases of up to a factor of ten under bias. These changes could be explained in terms of SCLC. Group II crystals, exhibitingI‐Vcharacteristic with a voltage exponent much greater than two, showed low‐frequency‐capacitance increases of up to a factor of 1000. This behavior cannot be understood in terms of SCLC flow, and a two‐layer model is proposed which provides a satisfactory explanation.