The effect of the Ge layer thickness on the Pd/Ge/Au/Ni/Au ohmic contact to n-InGaAs was investigated. The ohmic behavior was related to the variation of constituent phases in the ohmic contact metals-phase transformation. It was found that the formation of PdGe is more helpful than that of Pd2Ge to reduce the specific contact resistance. The AlGaAs/GaAs heterojunction bipolar transistors (HBTs) using the Pd/Ge/An/Ni/Au contact system showed a good RF performance. (C) 1999 Elsevier Science B.V. All rights reserved.