A civil lawsuit accuses Mogilyansky of helping finance an online child-sex ring and developing its English-language Web site to attract international customers.
"I still feel his repugnant breath. I hate him," one of the victims, now 18, wrote in a statement read in court.
Friends from Mogilyanksy's days at Columbia University also testified, describing him as a brilliant man of high character. His wife called him a loving husband and father. And a defense psychotherapist concluded that he is not a sexual predator.
But the victims wrote that he left them pained, depressed and unable to trust men since the assaults in 2003 and 2004.
Mogilyanksy received the top of the sentencing range negotiated as part of his plea to four "sex tourism" counts.
U.S. District Judge Mary A. McLaughlin decried "this business of going abroad to have sex with young girls." She found the defendant's accomplishments impressive but called his crimes "grave."
"To take young teenagers from that orphanage to an apartment and have sex with them is a grave criminal act," McLaughlin said.
Mogilyansky had lived in Richboro northeast of Philadelphia with his wife and their three toddlers until his bail was revoked following his arrest in December.
"This isn't me," Mogilyansky told the judge. "It wasn't until after I was arrested that I looked myself in the mirror and said, 'How could I have done this?"'
Prosecutors at the bail hearing estimated his wealth at $5 million to $10 million, and said he earned $750,000 a year.
But defense lawyer Jack McMahon scoffed Wednesday at the suggestion that his client remains a millionaire, and prosecutors did not challenge his request for a low fine of $12,500.
Mogilyansky must also pay each victim $5,000 restitution, register as a sex offender after his release and serve 15 years of federal probation.
More than 50 "sex tourism" cases have been brought in the U.S. under the 2003 Protect Act, which aims to prosecute Americans who travel overseas - beyond the reach of U.S. law - to have sex with children.