The two companies, currently owned by HTP Capital, provide heat recovery steam generators for combined-cycle power plants.
NEM primarily designs, engineers and sells heat recovery steam generators, while NES is in the associated service business.
Siemens said it has been working together with NEM and NES for years, most recently on the Dutch Enecogen, Diemen and Hemweg projects and on the T- Power project in Belgium.
The company will buy NES and take over the major part of NEM’s business, subject to approval by the anti-trust authorities.
NEM CEO Gerard Dijk said the addition to the Siemens Group provides NEM with access to the international network of Siemens.
"Siemens, being a supplier of gas turbines, and NEM, supplier of heat recovery steam generators, are strongly complementary organizations. Altogether, this makes Siemens a very strategic partner to us," Dijk said.
The acquisition of NES and NEM business is subject to regulatory approval by the European Commission.
