During atomic layer deposition of high permittivity (high-k) metal oxide gate dielectrics, an interfacial layer (IL) containing SiOx between high-k dielectric and Si substrate is almost unavoidable. However, an Al(CH3)(3) (TMA) pretreatment for 3600 s on H-terminated silicon surface can effectively reduce the interfacial layer from 1.7 to 0.5 nm during atomic layer deposition of aluminum oxide. Interestingly, the surface TMA pretreatment increases the thickness of the initial IL during atomic layer deposition, but it greatly suppresses the final IL after 35 growth cycles. A reasonable mechanism is proposed based on the steric hindrance effect cofunctioning with the interfacial Al catalyzing effect.