Hawthorn has re-signed two key midfielders in the lead up to the do or die semi-final clash with Adelaide on Friday night.

Isaac Smith and Billy Hartung have both signed two-year contract extensions with the Hawks.

Smith, who was already contracted until the end of next season, will now remain at the Hawks until the end of 2018, while Hartung will remain in brown and gold until at least the end of 2017.

Smith, 26, has played 108 games in five years at the club, while the 20-year-old Hartung has played 25 games in two seasons.