The ohmic contacts to p-type GaAs formed by GaAs/Pt/Ti/Pt/Au systems were investigated. The specific contact resistance below 8 x 10(-7) OMEGA.cm2 was achieved when the interface Pt between GaAs and Ti/Pt/Au was thicker than 50 angstrom, which is about one-fourth of the conventional Ti/Pt/Au contact. The activation energies of the initial degradation of the Pt/Ti/Pt/Au electrodes correspond to the reaction of GaAs and Pt to form PtAs2. However, even after the initial degradation, Pt/Ti/Pt/Au with the thin Pt interface layer still shows lower contact resistivity. These systems are promising for practical p-type ohmic contacts for AlGaAs/GaAs heterojunction bipolar transistors.