Al2O3 insulator layer was deposited by atomic layer deposition (ALD) technique on p-type Si < 111 > and the Al/Al2O3/p-Si metal/insulator/semiconductor (MIS) structures were fabricated. The current-voltage (I - V) characteristics of these structures were investigated in two different temperatures. The main electrical parameters such as the ideality factor (n), zero bias barrier height (Phi(Bo(I - V))), and series resistance (R-s) values were found for 300 and 400 K. The energy density distribution profiles of the interface state density (N-ss) were determined from the I - V characteristics. In addition, the capacitance-voltage (C - V) and conductance-voltage (G/w - V) characteristics of devices were investigated in the frequency range 50-1000 kHz at room temperature. Frequency-dependent electrical characteristics such as doping acceptor concentration (N-A), energy difference between the valance band edge and bulk Fermi level (E-F), diffusion potential (V-D), barrier height (Phi(Bo(c - V))), the image force barrier lowering (triangle Phi(B)), maximum electric field (E-m), and R-s values were determined using C - V and G/w - V plots. In addition, the Nss values were performed using Hill-Coleman method. According to experimental results, the locations of N-ss and R-s have an important effect on I - V, C - V and G/w - V plots of MIS structure.