SEOUL, Oct 27 (Reuters) - A South Korean man who worked at Samsung Electronics' semiconductor unit and more recently at a pig farm has defected to the communist North by walking across the heavily mined border, the North's state media said on Tuesday.

Crossings are rare through the razor-wire and land-mined Demilitarised Zone buffer that divides the peninsula. But defections to the impoverished North from the affluent South are even rarer, with the last one likely taking place about four years ago.

The rival Koreas remain technically at war because they never replaced the armistice ending their 1950-53 conflict with a peace treaty.

"He is beside himself with joy for having accomplished this heroic deed," the North's KCNA news agency said. It identified the defector as Kang Dong-rim, 30.

South Korea's military and spy agency could not immediately confirm the report.

"He is now under the warm care of a relevant organ," KCNA said.

Since 2006, more than 2,000 North Koreans a year have defected to the South after crossing the longer and less perilous border with China. More than 16,000 North Koreans have defected to the South since 1953.

In 2005, KCNA said a man sailed through a volley of bullets to defect to the North. The South's military said at the time his family suspected he was drunk. (Reporting by Jack Kim; Editing by Jon Herskovitz and Nick Macfie)