The Hewlett Packard 4156A Precision Semiconductor Parameter Analyzer is an extremely useful tool for characterizing semiconductor devices. It has up to four probes that can serve as voltage sources, current sources, voltage monitors, and current monitors. These probes are designed to be programmed through a menu-driven user-interface. Possible measurements include, I-V curve of a simple two terminal device, Id-Vds-Vg graphs for MOSFETs, switching characteristics of logical gates, etc.