In this paper, AlN thin films with two different thicknesses, i.e., 7 and 47 nm, were deposited at 200 °C on p-type Si substrates by plasma-enhanced atomic layer deposition using trimethylaluminum and ammonia. To investigate the electrical characteristics of these AlN films, MIS capacitor structures were fabricated and characterized using current-voltage and high-frequency (1 MHz) capacitance-voltage measurements. The results showed that the current transport mechanism under accumulation mode is strongly dependent on the applied electric field and thickness of the AlN film. Possible conduction mechanisms were analyzed, and the basic electrical parameters were extracted and compared for AlN thin films with different thicknesses. Compared with 7-nm-thick film, a 47-nm-thick AlN film showed a lower effective charge density and threshold voltage along with a higher dielectric constant.