This book presents the magnetic, electrical and surface morphological characterization of AuGe/Ni/Au Ohmic contact metallization on GaAs/AlGaAs two-dimensional electron gas (2DEG) multilayer structures. These structures, have well known applications in infrared sources/detectors, high-speed electronic devices (HEMTs) and high sensitivity Hall effect magnetic field sensors. Deposition of AuGe/Ni/Au followed by rapid thermal anneal is a well tested recipe for Ohmic contact formation in these structures. Alternatives to Ni such as Cr or Ti may be used for Ohmic contact formation in sensors, where possible distortion of the measured field by the ferromagnetic Ni is an issue. Explicit studies of the magnetic properties of the processed Ohmic contact metallization structures are rare in the literature. The book describes process optimization wherein three parameters- magnetization, contact resistance and surface roughness- are taken into account. It also describes some new insights into the changes that take place during processing in the Ohmic contact metallization structure, prior to the alloyed-contact formation.