Abstract: An improved gate metal structure for compound semiconductor devices comprises sequentially a compound semiconductor substrate, a Schottky barrier layer, an insulating layer and a gate metal. The insulating layer has a gate recess. The surrounding and the bottom of the gate recess are defined by the insulating layer and the Schottky barrier layer respectively. The gate metal includes a contact layer formed on the insulating layer, covering the gate recess and contacted with the Schottky barrier layer at the bottom of the gate recess; a first diffusion barrier layer formed on the contact layer; a second diffusion barrier layer formed on the first diffusion barrier layer; and a conduct layer formed on the second diffusion barrier layer. Thereby the reliability of the compound semiconductor devices is enhanced.