The "hot-probe" experiment provides a very simple way to distinghuish between n-type and p-type semiconductors using a soldering iron and a standard multimeter.
The experiment is performed by contacting a semiconductor wafer with a "hot" probe such as a heated soldering iron and a "cold" probe. Both probes are wired to a sensitive current meter. The hot probe is connected to the positive terminal of the meter while the cold probe is connected to the negative terminal. The experimental set-up is shown in the figure below: