A substrate bonding apparatus for bonding a first substrate to a second substrate includes a first bonding chuck configured to fix the first substrate to a first surface of the first bonding chuck; a second bonding chuck configured to fix the second substrate to a second surface of the second bonding chuck, the second surface facing the first surface; a process gas injector surrounding at least one selected from the first bonding chuck and the second bonding chuck in a plan view, the process gas injector configured to inject a process gas between the first substrate and the second substrate when respectively disposed on the first bonding chuck and the second bonding chuck; and an air curtain generator disposed at an outside of the process gas injector in the plan view, the air curtain generator configured to inject an air curtain forming gas to form an air curtain surrounding the first substrate and the second substrate.