Microsemi Corporation provides semiconductor and system solutions for aerospace & defense, communications, data center and industrial markets.

Microsemi is headquartered in Aliso Viejo, California and has offices in California (Camarillo, Cupertino, Garden Grove, San Diego, San Jose, Santa Clara, Santa Rosa); Boulder, Colorado; Atlanta, Georgia; Beverly, Lawrence, and Lowell, Massachusetts; Allentown and Reading, Pennsylvania; Austin and Dallas, Texas; Ottawa, Canada; Macau, Shanghai and Shenzhen, China; Herlev, Denmark; Bruges, Belgium; Ennis, Ireland; Hod HaSharon, Israel; Manila and Cabuyao, Philippines; Caldicot, United Kingdom; and Hyderabad, India. This list does not include properties acquired together with PMC-Sierra.

Microsemi was founded in February 1959 in Culver City, California as MicroSemiconductor. It incorporated in Delaware on September 27, 1960. A trade catalog and price lists from this early period can be found at the Smithsonian Institution. In March 1963, A. Feldon represented Microsemiconductor Corp in the Advisory Panel of Suppliers at the IEEE session on "Components for Miniaturized Electronic Assemblies".
According to the Missiles and Rockets magazine, in 1964 "Molecular packaging of integrated circuits has been suggested by Microsemiconductor Corp. This would involve the same process the company uses for diodes it supplies to the Improved Minuteman program." Microsemiconductor is cited in 1965 as supplier of miniature silicon diodes that are "ideal to use as beam profile detectors or to measure depth-dose distribution of small collimated beams." by University of California's Ernest O. Lawrence Radiation Laboratory. In 1966, two of the company's engineers, E.S.Resnond and M.W. Stillwell, published a Production Engineering Measures Study, on High Voltage Oscillators. As of 1969, Microsemiconductor's address was still 11250 Plaza Court, Culver City, CA 90230.
On August 13, 1969, Standard Resources Corporation, from Copiague, New York, a close-end management investment company, filed at the U.S. Securities and Exchange Commission a request to merge with Microsemiconductor. This request disclosed that the major shareholders of Microsemiconductor as of May 31, 1969 were Arthur Feldon (31%), Steve Manning (31%) and Thomas C. Hall (10%). At the end of the proposed merger the company would retain the name Microsemiconductor. At the time, J.M. Kaplan's JemKap Inc owned 37.7% of the outstanding common shares of Standard, which would make him the owner of 18.9% of the surviving company. Standard Resources and Microsemiconductor merged in November 1969.

According to the Orange County Business Journal, "In 1971, the New York operation was spun off and Philip Frey Jr. was brought on from Teledyne Inc.'s semiconductor division in Hawthorne to head Microsemiconductor. At the time, the company had annual sales of about $500,000, almost entirely to defense industry customers. In 1972, the company moved from Culver City to Santa Ana, California. Microsemi still was almost exclusively a defense business in 1987, but by then sales were close to $50 million. That same year, the company did a $35 million convertible bond offering, the proceeds of which were used to acquire about a dozen companies, most of them struggling "bargain" buys. When the acquisitions began straining profitability, Frey didn't waste a lot of time admitting his mistake. In 1989, Microsemi began selling them off. Sales, which hit a then-high of $104 million in 1989, fell to $83 million by 1991. But they've grown almost every year since and are expected by analysts to exceed $150 million for the fiscal year just ended. (1996)"

On July 1, 1982, Jemkap Inc acquired 48.6% of Microsemiconductor Class A Stock., and Microsemisemiconductor acquired the Siemens Components Group in Scottsdale, Arizona.

Microsemiconductor renamed itself to Microsemi, in February 1983.

On March 9, 1986, Microsemi, at the time a supplier of "high-performance semiconductor diodes in a variety of military, industrial and commercial products", issued 2.5 million shares of common stock. Up until this time, Jacob M Kaplan of New York owned or controlled 38.4% of the company shares, and was 94 years-old. Microsemi raised $26 million in the stock sale. Jacob Merril Kaplan, who was a philanthropist, died in Manhattan, NY on July 20, 1987.

Microsemi was originally traded Over the Counter, commonly traded as MicrSm. On March 1, 1990 Microsemi joined the NASDAQ exchange.

On March 1, 1987 Microsemi sold $35M in convertible debentures.

Between 1986 and 1990 Microsemi acquired over 60% of the shares of 11 companies.

In June 1991 Microsemi created two join-ventures in Taiwan for packaging in Taiwan its component dies made in Santa Ana, California. Microsemi established its presence in Ireland in 1992 through the acquisition of a facility in Ennis Co. Clare. The Ennis facility's key competencies are the development, manufacturing and high reliability testing of semiconductors to meet stringent aerospace, satellite, medical and security standards.

In July 1992 Microsemi acquired Unitrode's semiconductor products division.

In February 1993 Microsemi's stock crashed 54%, because of a cash crunch. "Microsemi has been restructuring for several years as defense budget cuts have slowed its sales. In 1989, the company said it planned to sell or close 10 subsidiaries not related to its core business of manufacturing computer chips for use in electronics equipment ranging from military weapons to heart pacemakers. The company sold four subsidiaries, shut down one, combined two and retained three. The company took $20.5 million in write-offs during the past three years in connection with the restructuring."

In April 1994 Microsemi formed a joint venture in China with Shanghai Electrical Apparatus, with 60% of the joint-venture belonging to Microsemi.

Linfinity, whose CEO was Jim Peterson, was the first Integrated Circuit company acquired by Microsemi, in 1999.

On November 30, 2000 Microsemi promoted Jim Peterson to president and CEO. Jim Peterson was previously the president of Linfinity.

In 2001 Microsemi relocated its headquarters from Santa Ana, California to Irvine, California.

Between 2006 and 2011 Microsemi acquired a mix of space/hi-reliability focused companies (MDT, TSI, Babcock, Spectrum Microwave), defense/security focused companies (Endwave, White Electronics, Arxan, Brijot, AML), and also companies focused in discrete and IC power products for commercial applications (Advanced Power Technology, PowerDsine, Nexsem), as well as communications focused companies (PowerDsine, VT Silicon, Zarlink) a programmable logic company (Actel) and an ASIC design house foucsed on analog mixed-signal (ASIC Advantage).

In 2011 Microsemi relocated its headquarters from Irvine, California to Aliso Viejo, California.

In August 2012, Microsemi marked its 20 years of operations in Ireland by naming Ennis its European headquarters. It also announced the inaugural Microsemi Scholarship in Engineering at the University of Limerick. In addition, the company funded a high-profile science and aerospace engineering programme in St. Flannan’s school in Ennis. Microsemi works closely with the Industrial Development Authority (IDA Ireland), which is responsible for attracting and developing overseas investment in Ireland. Support from IDA Ireland was a key factor in the company’s decision to invest in the region.

Between 2012 and 2013 Microsemi acquired Timing companies (the timing business of Maxim Integrated Products, Symmetricom) in addition to Zarlink.

In November 2013, Jim Peterson promoted Paul Pickle to COO and president, retaining the CEO position, and accumulating the position of Chairman of the Board.

In 2014 Microsemi established a design group in Cork, Ireland, through the acquisition of Mingoa, which is focused on advanced system-on-chip (SoC) software and solutions with an emphasis on ARM processor-centric designs.

Between 2014 and 2015 Microsemi acquired communications and data-center focused companies (Mingoa, Centellax, Vitesse, PMC-Sierra).

In March 2016 Microsemi announced the divestiture of the defense-focused business units acquired between 2009 and 2011.

In April 2016 Microsemi announced the divestiture of its Broadband Wireless Division, which was previously part of PMC-Sierra for $21M.

In October 2017 Microsemi announced the acquisition of the timing business of Vectron International from Knowles for $130 Million.

Microsemi has been producing various electronic products, including high-performance and radiation-hardened analog mixed-signal integrated circuits, FPGAs, SoCs and ASICs; power management products; timing and synchronization devices and precise time solutions, voice processing devices; RF solutions; discrete components; enterprise storage and communication solutions, security technologies and scalable anti-tamper products; Ethernet solutions; Power-over-Ethernet ICs.

Microsemi has provided semiconductor solutions for numerous U.S. space programs dating back to the launch of the first Atlas rocket. Several of Microsemi’s space products were used in the historic landing of the Mars Curiosity Rover in 2012. Microsemi products were also used for mission critical applications such as launch systems, avionics, telemetry, navigation, drive control, mission computers, cameras and other instruments.

In 2009 Barry Minkow, co-founder of the Fraud Discovery Institute, and in prison between April 28, 2014 and June 6, 2019, published a report claiming that James Peterson, Microsemi's President and CEO, had not obtained a bachelor's degree or Masters of Business Administration as he had listed on his biography on STEC Inc.’s regulatory filings (as part of his board position with that company) and on a US government security clearance application. Peterson responded with a public statement saying he "categorically" denied the reports. The next day, the registrar of Brigham Young University advised that they had double-checked and had no records of Peterson ever having obtained any degrees. An independent inquiry was made on behalf of the board by the law firm Munger, Tolles & Olson, which confirmed that in fact Peterson had not earned either degree. As a penalty for misrepresenting his academic credentials, Peterson paid Microsemi a fine and forwent his 2008 bonus.

It has been reported that Microsemi's ProASIC3 A3P250 FPGAs have an embedded backdoor that cannot be disabled. Microsemi has denied this. There is extensive material from Microsemi explaining how proper design of its FPGAs can be used as countermeasures against DPA. Microsemi's 4th generation of FPGA's is the only one to be certified to withstand these attacks.