Schottky contacts of sputter-deposited tungsten film on Si-doped (100) GaAs have been interpreted by material parameters such as phase transformation of $eta$W-$alpha$W, interdiffusion behavior of W, Ga, and As, and defect recovery kinetics by using AES, SEM,X-ray diffractometer, 4-point probe and I-V measurement. Diffusion depth at W/ GaAs interface during two stage activationannealing was decreased in comparison with the normal activation annealing, which causes the increase of barrier height at W/GaAs interface. The first rules of temperaturedependence of interdiffusivities of Ga, As, andW are as follows ; $D_w=1.64X10^-1(m^2/sec)$, exp(-3.77(eV.$mol^-1$)/kT) $D_Ga=5.67x10^-3(m^2/sec)$ exp(- 3.45(eV.$mol^-1$/kT) $D_As=1.07x10^-4(m^2/sec)$ exp (-3.09(eV.$mol^-1$)/kT) The resistivity change of W film has been related to the defect concentration, impurity concentration, and phase composition ($alpha$Wand$eta$W). The oxygen atoms contaminated to W films during the deposition have a substential effect on the nucleation of $eta$W. The resistivity of W film is changed from $270mu extohm.cm$ to $180mu extohm.cm$in the temperature range of $400^circC$ to $550^circC$, which indicates the annihilation of sputtering induced imperfections during the annealing. The $eta$W$ ightarrow$$alpha$W transformation occurs between $600^circC$ and $700^circC$, corresponding to the resistivity change from $180mu extohm.cm$ to $50mu extohm.cm.$