It used to be that there were 2 semi-finals and the top 4 finishers in each race would qualify for the final.

Then in recent years, the trend has been to have 3 semi-finals with the 2 fastest in each automatically qualifying for the final along with the next 2 fastest times.

Now, I just saw the results of the Euro-U23 semi finals, and the qualifiers are the 3 top finishers in each of the 2 semis, plus the next 2 fastest times.

To me, this seems to be the best method of these 3. Less chance of someone getting left out if they were in the fastest heat; and less chance of someone qualifying if they were in a slower semi.

Plus, I think a semi-final by definition, should be one of 2 races, not 3.