This article shows that the thermal stability of an InGaP Schottky contact can be improved by the refractory metal WSiN. Both the electrical characteristics and interfacial reactions were estimated by the I-V (current-voltage method). scanning electron microscopy, atomic force microscopy, and Auger electron spectroscopy. The WSiN/InGaP shows excellent I-V characteristics, and the Schottky barrier height is 0.85 eV after annealing at 400 degrees C. Over 500 degrees C, an interfacial reaction occurs and the I-V characteristic becomes leaky. We present an interfacial reaction model that shows In atoms condense and an eutectic alloy with W is formed.