An object of the present invention is to provide a semiconductor layer (n-type semiconductor layer) which demonstrate an excellent thermoelectric conversion performance and exhibits n-type characteristics. Another object of the present invention is to provide a thermoelectric conversion layer formed of the n-type semiconductor layer and a composition for forming an n-type semiconductor layer. Still another object of the present invention is to provide a thermoelectric conversion element, which has the thermoelectric conversion layer as an n-type thermoelectric conversion layer, and a thermoelectric conversion module.The n-type semiconductor layer of the embodiment of the present invention contains a nanocarbon material and an onium salt represented by a specific structure.