A study is made of <i>p</i>-type HgCdTe surface passivation with ZnS. Measurements of capacitance-voltage characteristics for metal insulator semiconductor (MIS) devices show that the interface electrical properties strongly depend on the surface preparation. Under some appropriate surface pretreatment, the fixed interface charge density can be lowered to near -1 x 10<sup>11</sup> cm<sup>-2</sup>, and the slow trap density can be less than 1 x 10<sup>11</sup> cm<sup>-2</sup>, but the interface trap density is still as high as 10<sup>12</sup> cm<sup>-2</sup> eV<sup>-1</sup>. Experimental results are discussed.