Separate the onions into rings and set aside on a plate.
In a large bowl mix the flour, chili powder, cayenne, paprika, and salt.
Heat oil to a depth of about 4 inches in a heavy saucepan or deep fryer until it shimmers and a few drops of water sizzle when flicked into the oil.
Dredge a few onion rings at a time in the flour and fry until golden.
Drain on paper towels.
Repeat and fry the remaining onion rings.
Serve at once.