Embodiments are directed to a method of passivating a surface of a high-mobility semiconductor and resulting structures having a reduced interface defect density. A semiconductor layer is formed on a substrate. A surface of the semiconductor layer is contacted with a sulfur source including thiourea at a temperature of up to about 90 degrees Celsius to form a sulfur passivation layer on the surface of the semiconductor layer. A dielectric layer is formed on the sulfur passivation layer and a minimum of interface trap density distribution at an interface between the semiconductor layer and the dielectric layer is less than about 2.0×1011 cm−2 eV−1.