A challenging test for FETs is drain-to-source on-state resistance, or RDS (On). Typically, a MOSFET is designed to have a low RDS (On). Let's say we have a spec of RDS (On) < 100 mΩ. To generate a measurable voltage drop, say 50mV across a 100 mΩ resistance, 500mA current is required. So, this measurement requires a high-resolution voltmeter and a high-current source.
We can use a VI to pull current through the FET, but because of IR drop through the DIB traces, we cannot use the same VI to measure voltage. To ensure a accurate measurement at the FET drain/source, we need to use a full kelvin 4-wire connection and a high -resolution differential voltmeter as shown in the figure below.
DIB design considerations: