Delilah Hamlin and Amelia Hamlin were heating up the frigid streets of NYC Monday night in their sexy lingerie that left little to the imagination.

The sisters -- whose parents are reality star Lisa Rinna and actor Harry Hamlin -- hit the streets of Manhattan with temps in the 30s last evening ... but these sizzling hot siblings weren't about to get a chill.

Check out the photos ... Delilah sports a black corset with a matching cone bra, stockings and heels. She was also gripping a black purse and phone.

Amelia, on the other hand, is wearing a red bra with a furry sheer top. She's also wearing white tights, black lace gloves and black pumps.

Exactly where the two were headed was anyone's guess ... but their racy ensembles couldn't escape the paparazzi.

Side note ... Delilah and Amelia's get-ups were created as part of this year's New York Fashion Week, which extends from February 6 to 11.