The interfacial microstructure and electrical properties of the Pt/Ti ohmic contact to p‐In0.53Ga0.47As (Zn: 5×1018 cm-3) formed by rapid thermal processing (RTP) were intensively studied. Significant interdiffusion of Ti, In, and As across the interface, driven by RTP, occurred at temperatures of, or above, 350 °C for a heating duration of 30 s. A minimum specific contact resistance (9.0×10-6 Ω cm2) was achieved after heating at 450 °C. Cross‐sectional transmission electron microscopy of this sample revealed an interfacial reaction zone with complicated microstructure, and the dominant interfacial compound was identified to be InAs. Further increase in RTP temperature resulted in a change in the microstructure, and degradation of the contact resistance. The temperature‐dependence characteristic of the specific contact resistance of as‐deposited Pt/Ti contact to InGaAs revealed a thermionic‐emission‐dominated carrier‐transport mechanism with an effective barrier height ϕb, of 0.13 V. RTP treatment to the sample at elevated temperatures up to 450 °C decreased the temperature dependence of the contact resistance. This phenomenon strongly suggests a partial conversion of the dominant carrier‐transport mechanism across the contact area from thermionic emission to field emission. This was further verified by fitting the temperature dependence of the measured contact resistance to a phenomenological theory based on a linear combination of the two different types of carrier‐transport mechanisms operating at isolated area segments distributed uniformly across the interface.