Well, according to draftexpress their measurements are almost identical.
Semi
Height w/o Shoes 6'5 ¼"
Height w/ Shoes 6'6 ¾"
Weight 241
Wingspan 6'9 ¾"
Standing reach 8'6"
Crowder
Height w/o Shoes 6'4 ¾"
Height w/ Shoes 6'6 ½"
Weight 241
Wingspan 6'9 ¼"
Standing reach 8'6 ¾"
Semi is a bit taller (which isn't necessarily a bad thing for Crowder cause he is still tall/strong enough to play the SF position while at the same time it's easier for him to switch on guards).
Seems like Semi is more athletic as well.
(Semi)
no step vert 35''
max vert 40.5''
(Crowder)
no step vert 31''
max vert 34.5''
Having said all that, imo Crowder is nothing more than an average starter. The reason he was sought-after around the league was his amazing contract. If Crowder were paid let's say 14+ million a year, no one would be talking about him. Remember DeMarre Carroll in his Atlanta days? He got paid 14.5 mill per year in 2015 and no one is talking about him ever since.
In that regard, the next Crowder would have to be a 3+D SF outperforming his contract. Semi is a 3+D SF on the rookie scale till 2021, so yeah he may very well become the next Crowder. If I had to choose from players not on the rookie scale, I'd go with Tony Snell. Last summer he singed a 4-year $44,000,000 deal with the Bucks (although final year is a player option). He is shooting the lights out (51.5 3P% on 4.1 shots per game, 54.7 FG%), he guards multiple positions and he even has a 2.3/0.8 assist to turnover ratio. Obviously, it's still early in the season, but it looks like he has improved a lot compared to last year (even more so compared to his Bulls days).