A duplex penthouse once owned by “Law & Order: Special Victims Unit” star Mariska Hargitay that’s built around a golden dome on top of Manhattan’s O’Neill Building is now on the market for $11.5 million. That’s down from its $14 million asking price in 2016.

Hargitay, who is the daughter of Jayne Mansfield, bought the unit, at 655 Sixth Ave. in Chelsea, for $7.12 million in 2007, property records show.

She then sold it for $8.15 million in 2008, when she and her husband, “Younger” star Peter Hermann, moved their family uptown.

The buyers were the late New York real estate mogul Maurice Laboz and his wife, Ewa.

The four-bedroom spread measures 4,819 square feet and comes with 2,549 square feet of outdoor space. There’s also a 53-foot-long glass-walled great room that connects to the dome and two terraces.

The dome itself is now a study and media room, but could also be used as a bedroom.

Hargitay and Hermann just listed their townhouse, at 45 W. 84th St. on the Upper West Side, for $10.75 million, about what they paid for it. The 7,000-square-foot home sports six levels and five or six bedrooms (depending on how it’s arranged).

Corcoran’s Robby Browne, Chris Kann and Jennifer Ireland have the townhouse listing with Alexa Lambert from Stribling.

When Maurice Laboz died in 2015, he cut his wife out of his will because they were in the process of divorcing. But he made sure he kept a controlling hand from the grave on his two daughters, who will inherit $10 million apiece when they turn 35.

The listing broker is Robert Falcone, of Douglas Elliman.