Hey!

In cases like this when the final results have not been declared yet, you can mention your overall percentage/GPA till your last semester i.e. fifth semester.
One more option is that check the tentative date of declaration of result. I think you must be having an idea about the tentative month of result announcement. If the last date for filling up the application form is quite later, then you can wait for your result.

The better option is to include marks till 5th semester, so that you can fill the form easily on time.

Hope it helps!