The Korat 1 and 2 projects together comprise 90 Siemens 2.3MW turbines with 101-metre rotors. They are among the largest operating projects in Thailand.
Construction was completed in 2012 and 2013, and the wind farms have been serviced by Siemens since then.
Siemens will also add a "power curve update" to the 90 turbines in a bid to increase power output from the project by 2-5%.
Retrofit additions to blades and changes to the software will be made, Siemens said.
"By upgrading and modernising the wind turbines at Korat 1 and Korat 2, and by supporting both projects with our experienced and innovative service operations, we are helping extend the operational lifetime of these important clean energy-producing assets," said Siemens wind power generation services CEO Mark Albenze.
Thailand is looking to increase its share of renewable electricity from 12% to 25% by 2021, according to Siemens.