High-pressure hydrogen postannealing effects on the electrical and structural properties of the Pt-Er alloy metal gate on HfO2 film have been investigated. It is shown that high-pressure hydrogen postannealing causes the removal of microvoids formed near the interface between Pt-Er alloy and HfO2 film, resulting in the increase of gate electrode contact areas, causing the decrease of equivalent oxide thickness. It is further shown that high-pressure hydrogen postannealing plays a role in the reduction of PtOx and the interface trap density, leading to the negative shift of flatband voltage and the improvement of the HfO2 interface quality. (c) 2006 The Electrochemical Society.