The Apple co-founder criticised Kutcher, who has claimed to be a "kindred spirit" of Jobs, and even adopted his extreme diet regime in preparation for the film.
"I suspect a lot of what was wrong with the film came from Ashton's own image of Jobs," he wrote.
Kutcher has questioned Wozniak's motives and claimed that he is "being paid by another movie studio to help support their Steve Jobs film".
Wozniak was "extremely unavailable to us when producing this film," the star said.
Wozniak is reported to have met with Aaron Sorkin, who is adapting Walter Isaacson's official biography of the late Apple chief, who died in 2011 from cancer complications.
But Wozniak, who designed the hugely-successful Apple II home computer before quitting the company in 1987, called Kutcher's statements "disingenuous and wrong".
He wrote: "These are examples of Ashton still being in character ... I was turned off by the Jobs script. But I still hoped for a great movie."
Wozniak criticised the film's accuracy - "I felt bad for many people I know well who were portrayed wrongly in their interactions with Jobs and the company" - and argued that its portrayal of Jobs is too flattering, since it ascribes to him a business and technology genius, which he did not always possess.
"The movie ends pretty much where the great Jobs finally found product success (the iPod) and changed so many of our lives," Wozniak wrote.
"I'm grateful to Steve for his excellence in the i-era, and his contribution to my own life of enjoying great products, but this movie portrays him having had those skills in earlier times."
Stern's film has been accused of propagating the "myth" of Jobs' untouchable genius.
Kutcher said his take on Jobs "isn't always a flattering portrayal".
The film covers Jobs' early experimentation with LSD and includes examples of his arrogance and temperamental behaviour around colleagues.
The film failed to impress critics or moviegoers during its opening weekend.
Jobs grossed just $6.7 million, missing the US box office top five.
The film has a score of just 25 per cent on the Rotten Tomatoes website which aggregates reviews.
The Huffington Post's Sandy Cohen said Jobs focused too much on Apple the company and not enough on Steve Jobs.
- The Independent