For the first time, the combination of the homoleptic erbium tris-guanidinate metalorganic complex ([Er(NMe₂-Guan)₃]) simply with water yielded high quality Er₂O₃ thin films on Si(100) substrates employing the atomic layer deposition (ALD) process. The process optimization to grow good quality Er₂O₃ layers was performed by varying the Er precursor pulse time, water pulse time and purge time. The high reactivity of the Er compound towards water and good thermal stability in the temperature range of 150-275°C (ALD window) resulted in homogeneous, stoichiometric Er₂O₃ layers with high growth rates (1.1 Å per cycle) and the as-deposited films crystallized in the cubic phase. The saturation behavior at different temperatures in the ALD window and the linear dependence of film thickness as a function of precursor pulse time confirmed the true ALD process. The potential of Er₂O ₃ thin films as gate dielectrics was verified by performing capacitance-voltage (C-V) and current-voltage (I-V) measurements. Dielectric constants estimated from the accumulation capacitance were found to be in the range of 10-13 for layers of different thicknesses (15-30 nm).