The two-time world champion has struggled with a largely uncompetitive car this year.
However, the Woking based team delivered an update for the most recent Grand Prix in Hungary and secured their best results of the season so far.
Both Alonso and Stoffel Vandoorne qualified in the top 10, and the Spaniard finished the race in sixth place.
But Alonso says the team have underachieved.
"As a team we can't be happy with the season so far," he said. "We were making it into Q3 normally last year, ninth/10th was our average position whereas this year we struggled a bit more."
Alonso also raced in the Indy 500 in May and missed the Monaco race, which has been one of his season's highlights.
"I had the Indy 500 which was a nice experience. So (it’s been a) fantastic first half of the season."