Arsenic trisulfide is the inorganic compound

Arsenic trisulfide is the inorganic compound with the formula As2S3. It is a dark yellow solid that is insoluble in water. It used as a pigment called King's yellow. It is produced in the analysis of arsenic compounds. It is a group V/VI, intrinsic p-type semiconductor and exhibits photo-induced phase-change properties. The other principal arsenic sulfide is As4S4, a red-orange solid known as the mineral realgar.

It is used in the manufacture of glass, oil cloth, linoleum, electrical semi-conductors, photoconductors, and fireworks, as a pigment, and in tanning and pesticides. Realgar was used by firework manufacturers to create the color white in fireworks prior to the availability of powdered metals such as aluminium, magnesium and titanium. It is still used in combination with potassium chlorate to make a contact explosive known as "red explosive" for some types of torpedoes and other novelty exploding fireworks branded as 'cracker balls', as well in the cores of some types of crackling stars. Realgar is toxic. It is sometimes used to kill weeds, insects, and rodents, even though more effective arsenic-based agents are available. Realgar was commonly applied in leather manufacturing to remove the hair from animal pelts. Because realgar is a known carcinogen, and an arsenic poison, and because competitive substitutes are available, it is rarely used today for this purpose.