The properties of metal oxides with high dielectric constant (k) are being extensively studied for use as gate dielectric alternatives to silicon dioxide (SiO2). Despite their attractive properties, these high-k dielectrics are usually manufactured using costly vacuum-based techniques. In that respect, recent research has been focused on the development of alternative deposition methods based on solution-processable metal oxides. Here, the application of the spray pyrolysis (SP) technique for processing high-quality hafnium oxide (HfO2) gate dielectrics and their implementation in thin film transistors employing spray-coated zinc oxide (ZnO) semiconducting channels are reported. The films are studied by means of admittance spectroscopy, atomic force microscopy, X-ray diffraction, UV–Visible absorption spectroscopy, FTIR, spectroscopic ellipsometry, and field-effect measurements. Analyses reveal polycrystalline HfO2 layers of monoclinic structure that exhibit wide band gap (≈5.7 eV), low roughness (≈0.8 nm), high dielectric constant (k ≈ 18.8), and high breakdown voltage (≈2.7 MV/cm). Thin film transistors based on HfO2/ZnO stacks exhibit excellent electron transport characteristics with low operating voltages (≈6 V), high on/off current modulation ratio (∼107) and electron mobility in excess of 40 cm2 V−1 s−1.