The nearest I can think of is bandant(e):

Elle est si bandante que je la mettrais bien dans mon lit ce soir.

No direct relationship to heat in bandante, but a direct reference to the male organ in erection.

Baisable is another possibility (from baiser (“fuck”) ). But the word does not convey such a strong urge as bandante.

Note that both words are very informal, probably more than “hot” because of their direct sexual significance.

“Bandante“, “Baisable” are disrepectfull for women. You can’t (and shoudln’t) say it to her face without taking a slap. It’s related to fuck (baisable = fuckable).

The slang the most use by my generation (18-30 yo) is “Bonne“. It still keep a bit of disrespect but you can use it among friends without being the redneck of the group. “Bonne” comes from “bonne à baiser” (good to fuck) but it has lost more and more its sexual connotation.

If you want to say to a girl she’s hot, you can say sexy.

To summarize:

• Bonne : among friends or with a girl you know well.
• Sexy: without any disrepect

The best equivalent I find is “canon” because it is not especially sexual and is of the same ‘language politeness level’.

I mean that it’s not particularly slang but you wouldn’t hear it in any formal context.

It is an adjective :

Scarlett Johansson est canon.

Or a noun, by the way Smoking hot could be :

Keira Knightley est un super canon.

I guess it comes from the expression “canons de beauté” which mean the reference criteria (to decide what is beautiful) commonly and currently accepted.

My explanation aren’t very clear but the equivalent of “hot” is definitely “canon”.

It’s probably as dated as I am, but B. Bardot was “une bombe.”

Canon comes to mind, although probably more used by 30+ y/o generations than younger people.

Cette fille / ce mec est carrément canon

In “today’s” language, hot would be somewhere between charmant/e/ (cute-ish, not rude but may convey sexual / flirty allusion) and bonne (used for women only, more disrespectful, sexist). I can’t think of a strict equivalent.

I am here assuming that the goal is to properly address a woman.
If not, then all the slang words previously proposed are fine (if used among friends only), bonne being the more common.
Otherwise, I concur that canon might be the closest translation although it is clearly outdated.
Using the word sexy is probably a bit more modern.
But in truth we Frenchmen do not have (to my knowledge) this particular concept available on our language.
Hope I’ve been useful.