SunEdison, Inc. (formerly MEMC Electronic Materials) was a renewable energy company headquartered in the U.S. In addition to developing, building, owning, and operating solar power plants and wind energy plants, it also manufactures high-purity polysilicon, monocrystalline silicon ingots, silicon wafers, solar modules, solar energy systems, and solar module racking systems. Originally a silicon-wafer manufacturer established in 1959 as the Monsanto Electronic Materials Company, the company was sold by Monsanto in 1989.

It is one of the leading solar power companies worldwide, and with its acquisition of wind energy company First Wind in 2014, SunEdison became the leading renewable energy development company in the world. In 2015, SunEdison sold off its subsidiary SunEdison Semiconductor, marking the completion of SunEdison's transition from a semiconductor-wafer company to a dedicated renewable-energy corporation.

Following years of major expansion and the announcement of the intent—which eventually fell through—to acquire the residential-rooftop solar company Vivint Solar in 2015, SunEdison's stock plummeted, and its more than $11 billion in debt caused it to file for Chapter 11 bankruptcy protection on April 21, 2016, eventually emerging in December 2017 as a restructured, smaller, private company.

The establishment of Monsanto Electronic Materials Company (MEMC), a silicon wafer–manufacturing division to serve the emerging electronics industry, was announced on August 6, 1959, as an arm of the U.S.-based multinational corporation Monsanto. In February 1960 MEMC started production of 19mm silicon ingots at its location in St. Peters, Missouri, 30 miles west of Monsanto's headquarters in St. Louis. As one of the first companies to produce semiconductor wafers, MEMC was a pioneer in the field, and some of its innovations became industry standards into the 21st century. MEMC used the Czochralski process (CZ process) of silicon crystal production, and developed the Chemical Mechanical Polishing (CMP) process of wafer finishing. In 1966 MEMC installed its first reactors for the production of epitaxial wafers, and developed zero-dislocation crystal growing, which made large-diameter silicon crystals possible.

In the early 1970s, MEMC opened a production plant in Kuala Lumpur, Malaysia, and sent its St. Peters–produced 2.25-inch ingots there for slicing and polishing. In 1979, MEMC became the first company to manufacture 125mm (5-inch) wafers; in 1981 the first to produce 150mm (6-inch) wafers; and, in partnership with IBM, in 1984 the first to produce 200mm (8-inch) wafers. In 1986 MEMC opened its production and R&D facility in Utsunomiya, Japan to serve the Japanese semiconductor market, becoming the first non-Japanese wafer maker with manufacturing and research facilities in Japan.

MEMC experienced heavy price-pressure from Japanese competition during the mid 1980s. Despite its success and increasing revenues, MEMC had to account for losses for a few years, leading to the decision of Monsanto, which was refocusing on chemicals, agriculture, and biotechnology products, to sell the electronic materials division. In 1989 the German company Hüls AG, the chemicals arm of the German conglomerate VEBA, acquired Monsanto Electronic Materials and combined it with Hüls' previous acquisition Dynamite Nobel Silicon (DNS) to form MEMC Electronic Materials. DNS already operated silicon wafer plants in Merano and Novara, Italy and integrated them within the new MEMC Electronic Materials. Hüls supported the new subsidiary with $50 million, for research and development and for manufacturing expansion. In 1991 MEMC developed the first process using granular polysilicon, which provided cost and productivity advantages over "chunk" polysilicon. Four years later MEMC acquired Albemarle Corporation's granular polysilicon production facility in Pasadena, Texas, which had been producing granular polysilicon since 1987.

MEMC's stock began trading on the New York Stock Exchange with an initial public offering in 1995. The IPO raised over $400 million, which went to finance an aggressive growth plan and repay some of the debt to its parent company, and Hüls/VEBA retained a majority interest in the company.

The cyclical downturn in the semiconductor business in the late 1990s hit MEMC hard. In 1998 the company reported a loss of $316 million on revenues of $759 million. In June 2000 VEBA AG, still holding 72% of MEMC, was merged with VIAG to form the new E.ON AG. E.ON wanted to focus on its core business of electric utilities, and assigned Merrill Lynch to sell MEMC. Merrill was unable to find a buyer until MEMC announced that it was on the verge of illiquidity in the middle of 2001. Finally in October 2001 E.ON was able to agree on a deal with the private equity company Texas Pacific Group (TPG), which purchased E.ON's stake in MEMC for a symbolic dollar and offered MEMC $150 million in credit lines. TPG restructured MEMC's debt, increased its stake in the company to 90%, and cut one third of its workforce.