The present invention is a semiconductor nanoparticle composed of a semiconductor crystal of a compound containing Ag, Au and S as essential constitutional elements. A AgAuS-based compound constituting the semiconductor nanoparticle has a total content of Ag, Au and S of 95 mass% or more. In addition, the compound is preferably a AgAuS ternary compound represented by the general formula Ag (nx) Au (ny) S (nz) . In the formula, n is any positive integer. x, y and z represent proportions of the number of atoms of the respective atoms of Ag, Au and S in the compound and are real numbers satisfying 0