The defender, who is known as the ‘Rock of Gibraltar’ was expected to be given a two-match ban for his red card for a professional foul in the quarter-final against Nigeria.
But the Confederation of African Football (CAF) has instead given Mensah a one-match suspension, ruling him out of the semi-final against Cameroon only.
He was sent off for bringing down Osaze Odemwingie, who was on a run at goal.
The only other red card of the tournament so far was shown to Guinea captain Pascal Feindouno, who was given a two-match ban for violent conduct.