Pd/Si/Ti/Pt and Pd/Si/Pd/Ti/Au ohmic contacts to n-type InCaAs were investigated for applications to AlGaAs/GaAs HBT emitter ohmic contacts. In the Pd/Si/Ti/Pt ohmic contact, as-deposited contact showed non-ohmic behavior, and high specific contact resistivity of $5 imes10^{-3}Omega extrm{cm}^2$ was achieved by rapid thermal annealing at $375^{circ}C$/10 sec. However, the specific contact resistivity decreased remarkably to $2 imes10^{-6}Omega extrm{cm}^2$ by annealing at $425^{circ}C$/10sec. In the Pd/Si/Pd/Ti/Au ohmic contact, minimum specific contact resistivity of $3.9 imes10^{-7}Omega extrm{cm}^2$ was achieved by annealing at $400^{circ}C$/20sec. In both ohmic contacts, low contact resistivity and non-spiking planar interface between ohmic materials and InGaAs were maintained. Therefore, these thermally stable ohmic contact systems are promising candidates for compound semiconductor devices. RF performance of the AlGaAs/GaAs HBT was also examined by employing the Pd/Si/Ti/Pt and Pd/Si/Pd/Ti/Au systems as emitter ohmic contacts. Cutoff frequencies were 63.9 ㎓ and 74.4 ㎓, respectively, and maximum oscillation frequencies were 50.1 ㎓ and 52.5 ㎓, respectively. It shows very successful high frequency operations.