The effects of Mg incorporation into La2O3 dielectrics on the electrical characteristics of metal oxide semiconductor (MOS) capacitors and field effect transistors (FETs) have been examined. Large negative shifts in flat band voltage (Vfb) for capacitors and threshold voltage (Vth) for FETs observed at a small equivalent oxide thickness (EOT) of below 1.4 nm can be well suppressed with the incorporation of Mg. Moreover, interfacial state density (Dit) at a small EOT can be decreased as well. The effective mobility (μeff) evaluation revealed a large improvement, particularly at a low effective electric field (Eeff). This improvement is considered to be due to the suppression of remote Coulomb scattering in the gate oxide with Mg incorporation.