Abstract: A method is provided for forming a through substrate via in a compound semiconductor having a transistor on a front side of the substrate. The method comprises forming a protective stop pad over a contact area on the front side of the substrate, forming a contact pad overlying the protective stop pad, such that the contact pad is in contact with a terminal of the transistor and plasma etching a backside of the substrate to form a contact coupling via to the protective stop pad. The method further comprises performing a chemical wet etch to remove the protective stop pad and depositing a conductive contact layer in the contact coupling via to provide a conductive contact to the contact pad.