No; temporary HP is not actual HP.
The rules distinguish temporary hit points as separate and distinct from actual hit points (emphasis mine):
Some spells and special abilities confer temporary hit points to a creature. Temporary hit points aren't actual hit points; they are a buffer against damage, a pool of hit points that protect you from injury.
Because temporary hit points are separate from your actual hit points, they can exceed your hit point maximum. A character can, therefore, be at full hit points and receive temporary hit points.
As you can see, the rules clearly specify that temporary hit points aren't actual hit points. Thus, spells that affect characters based on their HP, such as sleep ("Creatures [...] are affected in ascending order of their current hit points"), power word stun ("If the target has 150 hit points or fewer, it is stunned."), and power word kill ("If the creature you choose has 100 hit points or fewer, it dies.") don't consider temp HP at all in determining whether the creature is affect.
Rules designer Jeremy Crawford unofficially confirms this answer in a 2017 tweet:
I did my best to search, but couldn’t find anything. Do Temporary Hit Points count for purposes of determining whether or not a creature is affected by Sleep or Power Word Kill?
Hit points and temporary hit points are never added together.
So no, temporary HP is not considered for the effects of those spells unless explicitly stated otherwise in the spell description. It's generally just a damage buffer, nothing more.