A chalcogen compound layer exhibiting ovonic threshold switching characteristics, a switching device, a semiconductor device, and/or a semiconductor apparatus including the same are provided. The switching device and/or the semiconductor device may include two or more chalcogen compound layers having different energy band gaps. Alternatively, the switching device and/or semiconductor device may include a chalcogen compound layer having a concentration gradient of an element of boron (B), aluminum (Al), scandium (Sc), manganese (Mn), strontium (Sr), and/or indium (In) in a thickness direction thereof. The switching device and/or a semiconductor device may exhibit stable switching characteristics while having a low off-current value (leakage current value).