The current transport mechanism of AlGaN/GaN Schottky diodes prepared by atomic layer deposition (ALD) was explored using current–voltage (I–V) and capacitance–voltage (C–V) measurements. The Schottky barrier height decreased and the ideality factor increased with increasing the temperature. Poole-Frenkel mechanism was found to rule the forward current conduction, involving the dislocation-related trap states in AlGaN layer. The activation energy of traps was estimated to be about 0.6 eV under high reverse bias, related with trap-assisted tunneling. Frequency dispersion in the C–V data was not significant. C–V hysteresis measurements with the sequential scans with increasing the maximum voltage in accumulation showed the increase in the flatband voltage shift, which was associated with the charge trapping occurring in the interfacial oxide layer near the AlGaN/GaN interface. This work suggests that the suppression of Ga–O formation during the initial ALD process is a critical factor to improve the device performance.