The centre-back made his senior debut in December, coming on for Ben White in the 83rd minute of a 3-0 Champions League win away to Club Brugge, becoming the fourth-youngest player in the club's history to feature in European competition at 16 years and 103 days old.
He went on to feature three times in Arsenal's FA Cup campaign, including a start against Mansfield Town, before catching Mikel Arteta's eye again during pre-season with performances against Como and Borussia Dortmund.
"It means a lot to me," Salmon said after putting pen to paper. "A lot of hard work went into this, a lot of ups and downs, but I'm so proud.
"I think it's a proud moment for my family as well, I think it's a reward for them as well, because they put so much time and effort into me. It's proof of their hard work as much as mine."
Salmon joined Arsenal's academy at Under-11 level in 2019 as an attacker, only switching to defence as his coaches at Hale End identified a different long-term role for him.
"I was an attacker in those days, so it was a bit different, but it was good," he said. "It sounds kind of cliched but it's a lot of ups and downs, a lot of tough times. Sometimes you really go through adversity, but it's built me to the person I am today, so I'm thankful for it."
Training alongside the first team has already left a mark on his development, he added. "It's always a good experience to be around them. You learn so much, not even just on the pitch, but off the pitch, about how they prepare and how they carry themselves. It's valuable, I'm so grateful for who I've got here."
Salmon was also part of the squad during Arsenal's run to a first Premier League title in 22 years last season, an experience he believes taught him what separates champions from the rest.
"Being around that was amazing. You see so many one-percents that go into it," he said. "It's a long season, so there's so many things that change and happen, but really keeping that level over that period of time, it takes a lot. It's a lot of little things that push you to be a champion."
Looking ahead, Salmon, who can play at centre-back or right-back, said: "I'm looking forward to attacking the season. I gave myself a good start, so let's see what it holds."