# N-CHANNEL VS. P-CHANNEL

The transistor we made last time is called an N-channel FET, because the conductive channel when it's turned on is made of temporarily N-type semiconductor. We can also make a transistor by swapping the roles of N and P.
The result is called a P-channel FET, and everything works the opposite way around. Instead of a positive voltage, it needs a negative voltage at the gate (relative to the source) to turn it on. The negative voltage attracts holes towards the gate, which temporarily form a P-type channel and allow conduction.
Try building this circuit. It's the same as the previous one except that it's upside down and uses a P-channel FET, which is made from a piece of N between two pieces of P+. Note the circuit symbol for a P-channel FET, which has a small circle on the gate to indicate that it turns on when the gate goes low rather than high. (The circle is a symbol generally used in logic diagrams to indicate negation.)
The end result is the same, however -- the output is the logical opposite of the input. We have another way of building an inverter, although it's no better than the previous one. So what's the point, you ask? We'll get to that on the very next page...