It is, but Semantic UI is better because it has a more quality design and more ready made, flexible modules to chose from.

Both are great, but if you can, pick Semantic UI. I love it.

Could you provide some specific examples? That's almost word for word what people say about Bootstrap, too, and it'd be nice to know what shaped your opinion.

Cards: http://semantic-ui.com/views/card.html vs. http://v4-alpha.getbootstrap.com/components/card/

SUI is more compact, aligned and feature rich.

Modals: http://semantic-ui.com/modules/modal.html vs. http://getbootstrap.com/javascript/#modals

Again, here my vote goes for SUI, it's cleaner and better designed.

Untreated Bootstrap is so widely used that without extra styling it looks just another UI with no personality. Design is a sensitive, subjective topic however. Sometimes you want that crude industrial look that Bootstrap has :)

That basic modal semantic ui is using is simply fantastic. Large file size or not, this is definitely on my list of frameworks to try now.

Dont't forget that with components turned off and with gzip turned on it can be around 80k.