Agilent Technologies B1500A Training Manual page 26

Why Four SMUs?
Four terminal MOS device
Only one configuration required
Speed up testing
Gate
VAR1
SMU3
The basic semiconductor device is the 4-terminal MOS transistor. By assigning an SMU to each
terminal, you have complete flexibility to make any measurement without having to change the
device hookup. No relays are required to switch any connection; this is all done by changing the
mode of the SMU from the front panel.
Drain
Source
Common
Constant
SMU2
5-6
Substrate
VAR2
SMU1
SMU4
Module 5
Basic Measurement