Pae Jun-Ho, known in the United States as Kenneth Bae, was arrested in November as he entered the northeastern port city of Rason.
"The Supreme Court sentenced him to 15 years of compulsory labour for this crime," KCNA said.
Pyongyang has not specified the basis of the crimes allegedly committed by Bae, who is believed to be a Korean-American tour operator.
KCNA said on Saturday when announcing his trial that Bae had "admitted that he committed crimes aimed to topple the DPRK (Democratic People's Republic of Korea)".
"The welfare of US citizens is a critical and top priority for this department. We call on the DPRK to release Kenneth Bae immediately on humanitarian grounds," deputy acting State Department spokesman Patrick Ventrell said on Monday.
Seoul-based activist Do Hee-Yoon has told AFP that he suspected Pae was arrested because he had taken photographs of emaciated children in North Korea as part of efforts to appeal for more outside aid.
US officials have pointed out Bae had entered the country on a valid visa, and admitted to concerns he could be used as a "political bargaining" chip.
In 2011, a US delegation led by Robert King, the US special envoy for human rights and humanitarian issues, secured the release of Eddie Jun Yong-Su, a California-based businessman, who had been detained for apparent missionary activities.
In 2010, former US president Jimmy Carter won plaudits when he negotiated the release of American national Aijalon Mahli Gomes, sentenced to eight years of hard labour for illegally crossing into the North from China.
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