Vacuum‐evaporated pure amorphous silicon films have been successfully hydrogenated in a Theta‐pinch plasma source to give high photoconductivity. Unlike films produced by glow discharge of silane gas, these films are highly stable against heat, intense light illumination, moisture, and other atmospheric contamination. Structural change in the bulk Si matrix being absent, a comparison of properties of films before and after plasma treatment can provide valuable information on pure hydrogenation effects.