The W/n-GaAs Schottky junctions A and B of area 1.75×l0-2 cm2 were fabricated by deposition of W on the chemically etched polished surfaces of n-GaAs samples by rf sputtering using a rf powers of 300 Watt for 30 min. The W contact B was subjected to a 90 min. thermal anneal at 390 °C. The room temperature I-V and C-V/f (with 200 Hz < f < 1 MHz) measurements were carried out for both the as-deposited and thermally annealed W/n-GaAs Schottky junctions A and B, respectively. From the direct I-V data, the values of 1.09 and 8.1×10-8 A for the ideality factor (n) and the reverse saturation current (Io), respectively, were estimated for the diode B, compared to the values of n=1.70 and Io=6.3×10-6 A for the diode A. The observed frequency dispersion in the zero bias capacitance in the diode B was attributed to fast interface states with a time constant, τ2=6 μs and density, Nss2=5.8×1010 eV-1cm-2, whereas, both the slow interface states (with τ1=4 ms and density, Nss1=7.8×1012 eV-1cm-2) and fast states (with τ2=1 μs and density Nss2=8.6×1010 eV-1cm-2) were responsible for the observed frequency variation of the zero bias capacitance in the diode A. For the forward bias values in the range 20-100 mV, the frequency dispersion in the measured capacitance suggested the presence of both the fast and slow interface states (with time constants differing by three orders of magnitude) in the as-deposited and the heat treated W/n-GaAs interfaces. Thermal anneal at 390 °C for 90 min. lowered the density of states at the W/n-GaAs interface by two orders of magnitude and resulted in the formation of a high quality rectifying W contact to n-GaAs with a rectification ratio of 1.4×104, a low Io and an ideality factor close to unity.