I am re-taking the 4th semester. How does that look in the eyes of a graduate school admission committee?
To the admissions committee:

You'll definitely want to explain it in your Statement of Purpose (or whatever the equivalent may be in your country). It will probably be noticed but there isn't anything you can do about it now except do better and possibly seek help about your issue if you haven't already.

Some relevant questions are Explaining bad grades in application: SOP or separate letter and How do I make a bad semester not look bad during my scholarship application?.

To employers:

This is highly dependant on the field and employer. In Computer Science/software engineering, from my experience, employers don't care. They care about your abilities and the only time they even want your transcript is to check off HR's requirement that he/she does indeed have a degree. Larger and more corporate companies may care more, but my horrible undergraduate transcript has passed many times without any question (as have my colleagues').