The 23-year-old, who scored 26 goals in 54 games last season, had been widely linked with a move away from the club this summer.
A transfer did not materialise, but Wells has continued his form into the new season, netting seven times in as many games thus far.
"The transfer window has now passed and we have managed to keep hold of him, which is a credit to the board," Parkinson told reporters at a press conference.
"It is also a credit to Nahki because not once has he banged on my door wanting to know about any moves or speculation about him. He has just got on with his job. For such a young lad, that is a great credit to him and his family.
"I have dealt with young players before who have been linked with moves away and it can be not easy. Nahki's focus has been top class."
Queens Park Rangers had been widely linked with a move for the striker.