"I know, I know, the old folks love him," Jennings said of Trebek in a July 19 letter titled "Dear Jeopardy."
Trebek, 66, who grew up in Sudbury, Ont., has hosted the show since 1984. Jennings, a software engineer from Salt Lake City, won $2.5 million during his 74-game winning streak on "Jeopardy!" in 2004.
He also took aim at what he said were the show's "effete, left-coast" categories and "same-old" format.
"You're like the Dorian Gray of syndication," he wrote. "You seem to think 'change' means replacing a blue polyethylene backdrop with a slightly different shade of blue polyethylene backdrop every presidential election or so."
After reports of his comments appeared in the media Tuesday, Jennings countered on his Web site that his letter was meant to be "a humor piece."
"For the record: I've loved 'Jeopardy!' since I was a kid, as anyone who talks to me for about five minutes knows. Making goofy jokes about TV shows isn't 'bashing.' I believe it's the whole reason Al Gore invented the Internet."
Jennings also responded Tuesday to people who posted comments on his Web site's message board, calling them "humor-impaired sock puppet users."