There are equivalent P-channel devices, just as there are PNP and NPN bipolar transistors. Were you to bias an n-channel JFET as you would a bipolar transistor with a positive bias on its gate ...

In this module on MOSFETs (metal-oxide-semiconductor field-effect transistors), we cover the following topics: History of the development of MOSFETs, Device structure, Device types, Circuit symbols, ...