The first hydrogenated amorphous germanium and hydrogenated amorphous silicon‐germanium alloy field‐effect transistors with appreciable field‐effect response inn‐ andp‐channel modes were developed by reducing the dihydride content in the films. Field‐effect mobilities were derived from transistor characteristics. Hole mobilities are superior to those in pure hydrogenated amorphous silicon which offers the opportunity for improved thin‐film devices.