Peterson faced a maximum 60-year prison term. He was given four years of credit for time served since his arrest. Illinois does not have the death penalty.
Peterson was convicted in September in the 2004 death of Kathleen Savio, 40. She was found dead in a dry bathtub with a 2-inch gash on the back of her head. The 38-year sentence was handed down Thursday.
Peterson is also suspected in the disappearance of his fourth wife, Stacy Peterson, who was 23 when she was last seen.
Authorities reopened the Savio case as a homicide after Stacy Peterson's disappearance.
Drew Peterson was denied a defense-requested retrial by the judge earlier Thursday.
Fascination nationwide with Peterson arose from speculation he sought to use his law enforcement expertise to get away with murder.
Peterson shocked the courtroom during his sentencing hearing by shouting, "I did not kill Kathleen!" as he made a statement to the court.
Someone in the court audience responded by shouting back, "Yes, you did," and the person was then removed from the room.
A turning point at the trial came when the defense called a divorce attorney who said he spoke to Stacy Peterson before she vanished. Rather than blunting her credibility, the witness stressed to jurors that Stacy Peterson seemed to truly believe her husband killed Savio.
Before his 2009 arrest, the glib, cocky Drew Peterson seemed to taunt authorities, suggesting a "Win a Date With Drew Contest" and then, after his arrest, "Win a Conjugal Visit With Drew Contest." More recently, his story inspired a TV movie starring Rob Lowe.
Savio's death was initially deemed an accident. After Stacy Peterson vanished in 2007, Savio's body was exhumed and re-examined.
Drew Peterson had divorced Savio a year before her death. His motive for killing her, prosecutors said, was fear that a pending settlement would wipe him out financially.
Prosecutors suspect Peterson killed his Stacy Peterson because she could finger him for Savio's death, but her body has never been found and no charges have ever been filed. Jurors weren't supposed to link her disappearance to Savio's death, and prosecutors were prohibited from mentioning the subject.
Peterson has maintained his fourth wife ran off with another man and is still alive.
Prosecutors faced enormous hurdles as they tried Peterson for Savio's death.
They had no physical evidence tying him to her death and no witnesses placing him at the scene. They were forced to rely on typically barred hearsay - statements Savio made to others before she died and that Stacy Peterson made before she vanished. Illinois passed a hearsay law in 2008 tailored to Peterson's case, dubbed "Drew's Law," which assisted in making some the evidence admissible at Peterson's trial.
The hearsay - any information reported by a witness not based on the witness' direct knowledge - included a friend testifying that Savio told her Peterson once put a knife to her throat and warned her, "I could kill you and make it look like an accident."
Peterson's attorneys have said they might appeal all the way to the U.S. Supreme Court on grounds the hearsay law is unconstitutional.
The Associated Press contributed to this report.
