A Long Island man has been convicted of beating his month-old son to death and faces up to 25 years in prison.

According to the Suffolk County District Attorney’s Office, a jury convicted the 32-year-old Kings Park man of first-degree manslaughter and endangering the welfare of a child four years after the boy, who was 43 days old, was killed.

The defendant, Christopher Foster, was found not guilty of second-degree murder.

The DA’s office said in a press release that an autopsy showed infant Jonathan Hertzler had suffered a fractured skull, four broken ribs and bruises on his face. When he died on Oct. 11, 2011, his fatal injuries had been caused by multiple blows.

Clarissa Hertzler, the boy’s mother, testified that Foster often became angry when the baby cried, the DA’s office said, and the infant “was a source of constant aggravation.”

According to the DA’s office, Assistant District Attorney Dana Brown told the jury that the night the baby died, Foster was the last person to hold him. She said Foster called his boss — not 911 — to report Jonathan was not breathing.

First-degree manslaughter is a Class B felony, and is defined as occurring when an adult intends to cause physical injury to someone younger than 11 years old and “recklessly engages in conduct which creates a grave risk of serious physical injury … and thereby causes the death of such a person,” the DA’s office said.

Foster was remanded to the county jail and will be sentenced on Sept. 8. He faces up to 25 years in state prison.