We report a sharp reduction in the resistivity of Ohmic contacts using in situ deposition of molybdenum (Mo) contacts onto n-type In0.53Ga0.47As grown on InP. The contacts were formed by evaporating Mo onto the wafer using an electron beam evaporator connected to a molecular beam epitaxy chamber under ultrahigh vacuum. Transmission line measurements showed specific contact resistivities of 0.5±0.3 Ω μm2 (2.90 Ω μm), 0.9±0.4 Ω μm2 (4.3 Ω μm), and 1.3±0.4 Ω μm2 (4.7 Ω μm) for Mo on abrupt InAs/InGaAs heterojunctions, graded InAs/InGaAs, and InGaAs films, respectively. These low resistances meet the requirements for terahertz transistors.