The parameter known as the modified sheet resistance Rsk has been used in the modeling of ohmic contacts to define the region of alloying/reaction immediately below the metallization. In this study, the value of Rsk has been measured for Pd/Zn/Pd/Au, Pd/Au, Zn/Pd/Au, Au/Zn/Au, Ni/Zn/Ni/Au, Cr/Au, and Pd/Mn/Sb/Pd/Au contacts to In0.47Ga0.53As/InP as a function of the annealing temperature to 500 °C. In the as‐deposited contacts, the measured value of Rsk was lower than the sheet resistance outside of the contact, Rsh, by a factor of ∼2 to 3. This reduction in Rsk from Rsh has been attributed to (a) the formation of low‐resistivity phases at the interface and (b) the creation of a doped region by indiffusion of the Zn. In addition, in the Pd/Zn/Pd/Au contacts, the effect of varying the thickness of the layer of Zn between 0 and 400 Å on Rsk was examined. A thickness of Zn≥50 Å was required in order to produce a significant reduction in Rsk from the value for the Pd/Au (Zn=0 Å) contacts. This effect was enhanced by annealing at 500 °C, which produced a value of Rsk lower than Rsh by a factor of ∼10. The reduction in Rsk by annealing treatment was consistent with an enhanced formation of the interfacial phases and an increase in the rate of indiffusion of the Zn. The exceptions to these trends were in the Pd/Mn/Sb/Pd/Au contacts which showed an approximately constant value of Rsk and Pd/Au which showed a minor reduction in Rsk with increase in annealing temperature. © 1995 American Institute of Physics.