The electrical properties of HfxAlyO compound dielectric films and the HfxAlyO/InGaAs interface are reported for various dielectric film compositions. Despite the same trimethylaluminum (TMA) pre-deposition treatment, dispersion in accumulation and capacitance-voltage (C-V) hysteresis increased with hafnium content. Different kinds of border traps were identified as being responsible for the phenomena. After anneal, the density of states in the HfxAlyO/InGaAs interface varied quite weakly with dielectric film composition. The optimal composition for obtaining high inversion charge density in metal oxide semiconductor gate stacks is determined by a tradeoff between leakage and dielectric constant, with the optimum atomic cation ratio ([Hf]/[Al]) of ∼1.