Simonyi and two Russian cosmonauts, commander Mike Lopez-Alegria and flight engineer Mikhail Tyurin, the 14th crew of the International Space Station, landed safely in their Soyuz spacecraft in the steppes of Kazakhstan.
The landing had been delayed by 24 hours and moved farther south because wet ground at the initial site precluded helicopter operations.
Before closing the Soyuz station hatches at 2:03am on Saturday, Lopez-Alegria and Tyurin said farewell to the E15 crew, commander Fyodor Yurchikhin and flight engineers Oleg Kotov and Suni Williams.
Simonyi, 58, made his fortune heading up Microsoft's application software group, which developed the Microsoft Office suite including Word and Excel.
The computer scientist left Microsoft in 2002 to form his own firm called Intentional Software.
Simonyi paid $25m for the 12-day space flight.
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