A comprehensive study of the Schottky contacts on Ga0.51In 0.49P has been made. The Ga0.51In0.49P epitaxial layer was successfully grown on the GaAs substrate by low-pressure metal-organic chemical-vapor deposition to form a lattice-matched heterostructure. Three different types of films, including single-layer metal (Pt, Ni, Pd, Au, Co, Mo, W, Cr, Ti, Al, Ta, and In), metal silicides (WSi 2, W5Si3 PtSi, and Pt2Si), and TiW nitrides (TiWNX) as the Schottky contacts metals on Ga 0.51In0.49P were studied. Due to the high-band-gap nature of Ga0.51In0.49P, the Schottky contacts on Ga 0.51In0.49P demonstrate good characteristics. The barrier heights range from 0.79 to 1.19 eV depending on the selection of the metals and the annealing conditions. Among single-metal films, Pt film demonstrates the best thermal stability. A barrier height of 1.09 eV and an ideality factor of 1.06 were obtained even after the Pt Schottky diode was furnace annealed at 500 °C for 30 min. For refractory compounds, the TiWNX film with the highest nitrogen content shows the best thermal stability with a barrier height of 1.00 eV and an ideality factor of 1.04 even after high-temperature annealing at 850 °C.