In this paper, tungsten-based Schottky diodes on AlGaN/GaN heterostructures were fabricated employing reactive sputtering, enabling a controlled modulation of the Schottky barrier height (ΦB). By varying the flux ratios between N2 and Ar during deposition, the electrical properties of both Schottky diodes and high electron mobility transistor (HEMT) devices were tuned. Forward current–voltage (I–V) measurements revealed an increase in the homogeneous Schottky barrier height from 1.26 to 1.39 eV with increasing N2:Ar gas-flow ratio, with an ideality factor of about 2.6. Capacitance–voltage (C–V) measurements, performed to monitor the two-dimensional electron gas concentration (ns) and the threshold voltage (VTH), show a reduction in the carrier concentration (from 4.7 × 1012 to 4.0 × 1012 cm−2) and an increase in the threshold voltage (from −1.36 to −1.17 V) with an increase in the barrier height. The same W-based contacts were then implemented as HEMT gate electrodes. The higher barrier height reduced the gate leakage current by 1 order of magnitude at the cost of 8% reduction in the drain saturation current. These results demonstrate that reactive sputtering is an effective approach to engineer gate contacts in AlGaN/GaN devices.