The present invention relates to a semiconductor device comprising a semiconducting material, wherein the semiconducting material comprises a halometallate compound comprising: (a) cesium; (b) palladium; and (c) one or more halide anions [X]. The invention also relates to a layer comprising the semiconducting material. The invention further relates to a process for producing a halometallate compound of formula (IV): [A]2[MIV][X]6, which process uses a H[X] and a compound comprising a sulfoxide group.