An assembly is disclosed for releasably mounting a semiconductor package with respect to a rigid carrier, in a predetermined alignment with the carrier to protect the package leads and position the leads for electrical testing. Two substantially identical dielectric frames are positioned on opposite sides of the leads and fastened in a sandwich arrangement enclosing remote end portions of the leads. Registration openings, provided at opposed corners of the frames, receive registration pins projected from the carrier, thus to positionally align the package and carrier in transverse directions. Spring-loaded retainers engage a central body of the semiconductor package to retain the package against longitudinal movement relative to the carrier.