Atomic layer deposition (ALD) is a promising technology for fabricating conformal thin films of atomlevel thickness with chemical composition control over a variety of structures. This paper demonstrates the ALD of iron oxide thin films using a novel iron precursor, namely, bis[bis(trimethylsilyl)amide]iron [Fe(btmsa)2] and hydrogen peroxide as an oxygen source. The growth characteristics of iron oxide were investigated by varying the deposition temperatures from 100 to 225 °C, such that the ALD growth mode was observed at 150 to 175 °C with an average growth rate of 0.035±0.005 nm/cycle. The films deposited in ALD mode exhibited highly linear film thicknesses with the number of cycles and excellent conformality over high-aspect-ratio trenches. In addition, the deposited films were extremely pure and revealed a hematite phase without any subsequent heat treatment, even if the films were deposited at low temperatures.