The electrical properties of Au/Ti/HfO2/n-GaAs metal/insulating layer/semiconductor (MIS) contact structures were analyzed in detail by the help of capacitance-voltage (C-V) and conductance-voltage (G-V) measurements in the temperature range of 60-320 K. The HfO2 thin-film layer was obtained by atomic layer deposition technique (ALD). The main electrical parameters such as ideality factor (n) and barrier height (Phi(B0)) were determined for Au/Ti/n-GaAs and Au/Ti/HfO2/n-GaAs diodes using current-voltage (I-V) measurement at 300 K. The values of these parameters are 1.07 and 0.77 eV for the reference (Au/Ti/n-GaAs) diode and 1.30 and 0.94 eV for the Au/Ti/HfO2/n-GaAs MIS diode, respectively. An interfacial charge density value of Q(ss) = 4.14 x 10(12) Ccm(-2) for the MIS diode was calculated from the barrier height difference of Delta Phi = 0.94 - 0.77 = 0.17V. Depending on these results, the temperature-dependent C-V and G-V plots of the device were also investigated. The series resistance (R-s), phase angle, the interface state density (D-it), the real impedance (Z') and imaginary impedance (Z '') were evaluated using admittance measurements. The C and G values increased, whereas (Z '') and Z decreased with increasing voltage at each temperature. An intersection point being independent of temperature in the G-V curves appeared at forward-bias side (approximate to 1.4 V); after this intersection point of the G-V plot, the G values decreased with increasing temperature at a given voltage. The intersection points in total Z versus V curves appeared at forward-bias side (approximate to 1.7 V). The Nyquist spectra were recorded for the MIS structure showing single semicircular arcs with different diameters depending on temperature.