A semiconductor light emitting device package, includes: a ceramic substrate having first and second electrode structures; a light emitting diode chip mounted on the ceramic substrate, electrically connected to the first and second electrode structures, and configured to emit ultraviolet light; a sidewall structure disposed on the ceramic substrate, providing a cavity surrounding the light emitting diode chip, and including an alloy having a thermal expansion coefficient in a range of 2 to 10 ppm/° C. and a Young's modulus in a range of 100 to 300 Gpa; and a glass cover disposed on the sidewall structure to seal the cavity.