The award comes after Hernandez went 6-0 with a 1.52 earned run average after Sept. 1 - and was his second such award this season. Felix was also the Pitcher of the Month in June.
The leader of a staff that led the league with a 3.87 ERA this season, the 23-year-old finished the season 19-5 with a 2.49 ERA in 34 starts.
It marks the first time any Seattle pitcher has ever won two AL Pitcher of the Month awards in a season - and Jarrod Washburn, before being traded to Detroit, was named the July pitcher of the month.
That meant the Mariners won three of the six awards given this season to pitchers.