Pd/Ge ohmic contact system on n-type InGaAs was studied. A good ohmic begavior by rapid thermal annealing was shown up to $400^{circ}C$, and the specific contact resistance was reduced to low-$10^-6Omega extrm{cm}^2$EX>. However, above $425^{circ}C$ it was deteriorated by intermixing and phase reaction of ohmic metals and InGaAs substrate. No remarkable phase change was observed below $350^{circ}C$, but the reaction was initiated at ~$375^{circ}C$ and considerable phase change was found above $425^{circ}C$. Non-spiking and planar interfaces were observed even when annealed at $425^{circ}C$, and smooth and shiny surface was kept up to $400^{circ}C$.