“I know this sounds like it’s not true,” says Kaley Cuoco, “but as huge as the show is, it’s just part of my life — not my whole life.”

The Big Bang Theory is huge all right. Now in its sixth season (8 p.m. Thursdays on CBS), it reigns as TV’s hottest sitcom, centering on a gaggle of geeks who live across the hall from aspiring actress Penny (Cuoco).

Penny is no genius but neither is she a dumb blonde, which is key to the genius of Big Bang. “She’s obviously not book-smart,” says Cuoco, “but she’s street smart and good-hearted and can make fun of herself.”

Reflecting on what her hit sitcom has meant to other parts of her life, she mentions her parents. During her Southern California childhood, they often had to cut corners, but she “never noticed” when life was down.

“This year, I’m hosting Thanksgiving and Christmas with, like, 25 people at my house — I can do that now.” Her voice starts to tremble and her eyes moisten. “It’s emotional. The show has been the hugest blessing.”

Cuoco, who turns 27 Nov. 30, shot to fame on 8 Simple Rules for Dating My Teenage Daughter as the older daughter in a household headed by the late John Ritter as a bewildered, loving dad.

“I just adored him,” says Cuoco, unleashing a stream of memories of how he used to cut up on the set and how much she learned from him. “Working with him showed me that I loved sitcoms “I’m a Bridesmaids type girl. I love silliness. That’s who I am at heart.”