The temperature dependence of current-voltage (I-V) Schottky barrier heights (SBH) and ideality factors (n) in Ni-nGaAs high voltage (ND = 5 × 1014-1015 cm-3) diodes was measured in the temperature range 298-473 K. The I-V SBH Φ;B, increases slightly (by about 3.5%), and n decreases by about 5% when T is increased from 298 to 473 K. Consequently, the flat-band SBH ΦFB, approximated by the product ΦB × n decreases slightly with increasing temperature, in agreement with the capacitance-voltage SBH (ΦCV) behavior in similar diodes. The temperature coefficient of ΦFB is doping dependent, and equals ∼(1 ± 0.3) × 10-4 eV/K for ND = 5 × 1014 cm-3 and (2.2 ± 0.1) × 10-4 eV/K for ND= 1015 cm-3. Most of these results can be satisfactorily explained by the existence of laterally inhomogeneous barriers, as modelled previously. The most likely inhomogeneities are due to Ni-nGaAs reaction phases and interfacial crystallography. When literature data are re-evaluated using ΦFB instead of ΦB, much more consistent results are obtained, indicating that ΦFB always decreases (or at most stays constant) with increasing measurement temperature.