Yem Chrin`s charge had been reduced from murder to manslaughter. He said he was only trying to help the community.
Unlicensed doctors provide care in many parts of rural Cambodia.
Many are self-taught but poor medical facilities and funding mean they are often the only healthcare option for millions of Cambodians.
Spared life sentence
The number of people infected in the case has not been exactly determined. Estimates range from more than 100 to more than 270. The deaths of 10 people, mostly elderly, have been attributed to the infections.
Authorities detected the scale of the infections after a 74-year-old man tested positive for HIV in November last year.
Yem Chrin was arrested a month later. He admitted reusing syringes but denied he had intentionally spread the virus.
Provincial court judge Yich Na Chheavy said in the verdict: "The court found Yem Chrin guilty of operating health treatment without licence, injecting people with syringes that spread HIV and torturing people to die."
Reducing the charge to manslaughter had spared Yem Chrin a life sentence.
His lawyer, Em Sovann, told Agence France-Presse news agency: "My client still insists he is innocent. I will represent him if he wants to appeal this conviction."
Yem Chrin had reportedly practised in the area since 1996 and police said he was a well-respected doctor.
Cambodia suffered a high HIV prevalence rate in the 1990s but a safe-sex campaign has been successful in bringing it down from 2% in 1998 to 0.7% last year, UN figures show.
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