Hmm... great question!!
To be clear, Star Wars "Lazer shots" are not "lazers." The gun sends gas into a chamber where a Lazer heats the gas in to a plasma. That plasma is then compressed & then directed out of the barrel.
A plasma is a hot as lightning... & the Aliens biggest weakness seems to be fire, so I'm thinking it's effective... especially in light of that fact that Predator's plasma & pulse weapons are actually recognized as likely the best way to kill an alien & hold back hords of them... so I'm not sure what the difference would be between a SW's plasma weapon & those. Typical Storm trooper Blasters set to high Maximum power can blow a 2 foot hole in a thin metal door.
For sure SW's plasma weapons can kill them... the question would be "what size is necessary." The bigger the gun... the hotter & bigger the plasma will be... & the stronger the impact it will have. So a discussion regarding whether or not a star wars plasma shot can kill an alien would also have to include what size the weapon is.
To understand this better, it's probably simpler to understand that the plasma is as hot as lighting. It's amazing they can even contain a small shot in such a vessel as a pistol. It's the exact same technology with bigger/stronger guns... it just takes bigger & more hardware to contain the larger plasma. If you want to fire a larger plasma bolt with a handheld gun, you'll need extra barrels if you want to fire it again any time soon because they need time to cool. You'll need an added cooling device & extra power for that as well. You need a bigger chamber to contain & compress the larger plasma, so everything gets bigger the stronger the shot is.
Compound that by the size of Tie mounted blasters, then to ion canons mounted to star destroyers etc. At some point... & without a doubt... a SW's plasma will kill em.
I'm not trying to baffle you with technology of the SW's plasma shooting system... I'm just trying to be clear that if we're discussing this, that it's not exactly as simple as asking "Do SW's plasma shots penetrate Alien Exoskeleton." Size matters.
So if we doubt that a storm trooper rifle can't penetrate it, then Alien hasn't won yet because we can get larger hand-held guns or wall mounted guns, & you know what else they got? Fooking flame throwerz... & keep it going on up to calling in Tie fighters & targeting them from space wit teh fooking mega-ion canons. If we're still getting nowhere then shoot em wit teh fooking death star gun. I don't think anyone's gong to doubt that gets the job dun. At the very least there will be a bunch of aliens floating around in space because the planet is now dust. lol... Given their weakness to fire & predator's plasma guns though, I'm sure it would be way before that, even if not at the storm troooper rifle level.
So Vader wins in the end no matter how this discussion turns out.
That said... I'm legit curious to see what size of a gun it would take to penetrate an alien's exoskeleton.

I gotta split right now for a while though... What do you think? Predator's guns are pretty small, so I'm thinking hand held gets it dun.