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Founded1969; 53 years ago (1969) in Worcester, Massachusetts
  • L. J. Sevin
  • Louay E. Sharif
  • Richard L. Petritz
Defunct1985 (1985)
FateMerged into STMicroelectronics

Mostek was a semiconductor integrated circuit manufacturer, founded in 1969 by L. J. Sevin, Louay E. Sharif, Richard L. Petritz and other ex-employees of Texas Instruments. Initially their products were manufactured in Worcester, Massachusetts in cooperation with Sprague Electric, however by 1974 most of its manufacturing was done in the Carrollton, Texas facility on Crosby Road. At its peak in the late 1970s, Mostek held an 85% market share of the dynamic random-access memory (DRAM) memory chip market worldwide, until being eclipsed by Japanese DRAM manufacturers who offered equivalent chips at lower prices by dumping memory on the market.

In 1979, soon after its market peak, Mostek was purchased by United Technologies Corporation for US$345M. In 1985, after several years of red ink and declining market share, UTC sold Mostek for US$71M to the French electronics firm Thomson SA, later part of STMicroelectronics. Mostek's intellectual property portfolio, which included rights to the Intel x86 microprocessor family as well as many foundational patents in DRAM technology, provided a large windfall of royalty payments for STMicroelectronics in the 1990s.

Early calculator business[edit]

Early Mostek calculator on a chip

Mostek's first contract was from Burroughs, a $400 contract for circuit design.

The first design to be produced in their newly set-up MOS fab in Worcester, was the MK1001, a simple barrel shifter chip made using an aluminum-gate PMOS process. This was followed by a 1K DRAM, the MK4006, that was manufactured in their Carrollton facility. Mostek had been working with Sprague Electric to develop the ion implantation process which provided much better control of doping profiles, especially in lowering transistor threshold voltage. Using ion implantation, Mostek became an early leader in MOS manufacturing technology, while their competition was still mostly using the older bipolar technology. The resulting increased speed and lower cost of the MK4006 memory chip made it the runaway favorite to IBM and other mainframe and minicomputer manufacturers (cf. BUNCH, Digital Equipment Corporation).

In 1970 Busicom, a Japanese adding machine manufacturer, approached Intel and Mostek with a proposal to introduce a new electronic calculator line. Intel responded first, providing them with the Intel 4004, which they used in a line of desktop calculators. Mostek's device took longer to develop but was a single chip calculator solution, the MK6010. Busicom used the Mostek design in a new handheld line, the Busicom LE-120A, which went on the market in 1971 and was the smallest calculator available for some time.[1] Hewlett-Packard also contracted with Mostek for design and production of chips for their HP-35 and HP-45 calculators.

World leader in DRAM[edit]

Mostek's 4K Dynamic RAM.

Mostek co-founder Robert Proebsting invented DRAM address multiplexing with the MK4096 4096 X 1 bit DRAM introduced in 1973. Address multiplexing was a revolutionary approach which reduced cost and board space by fitting a 4K DRAM into a 16 pin package, while competitors took the evolutionary approach which led to a bulky and relatively expensive 22 pin package. Competitors derided the Mostek approach as unnecessarily complex, but Proebsting understood the future roadmap for DRAM memories would benefit greatly if only one new pin were needed for every 4X increase in memory size, instead of the two pins per 4X for the evolutionary approach. Computer manufacturers found address multiplexing to be a compelling feature as they saw a future 64K DRAM chip would save 8 pins if implemented with address multiplexing and subsequent generations even more. Per pin costs are a major cost driver in integrated circuits, plus the multiplexed approach used less silicon area, which further reduces chip cost. The MK4096 was produced using an NMOS aluminum-gate process with an added interconnect layer of polysilicon (dubbed the SPIN process)

The fear, uncertainty and doubt put up by the competition regarding address multiplexing was dispelled by the actual performance of the MK4096 which proved solid and robust in all types of computer memory designs.

In 1976 Mostek introduced the silicon-gate MK4027 (an improved version of the metal-gated MK4096), and the new MK4116 16K double-poly silicon-gate DRAM. They were designed by Paul Schroeder, who later left Mostek to co-found Inmos. From this point until the late 1970s Mostek was a continual leader in the DRAM field, holding as much as 85% of the world market for DRAM. The MK4027 and MK4116 were reverse-engineered by Mosaid and successfully cloned by many companies.

The 64K generation of DRAMs required a transition from 12 volt (and + and − 5 volt) to 5 volt-only operation, in order to free the +12 and −5 volt pins for use as addresses (the +5 volts and ground pins were assigned to pins 8 and 16, respectively, rather than the 16-pin TTL DIP standard of pin 8 for ground and pin 16 for +5 volts). While most competitors took a conservative approach by scaling the basic MK4116 design and process, Mostek undertook a major redesign which incorporated forward-looking features (such as controlled precharge current) that were not necessary at the 64K level and delayed their entry into the market. Mostek's 256K DRAM was further delayed by a then-ambitious two layer metallization design. When the price for 64K DRAMs collapsed in 1985, Mostek's 256K device was not ready for volume production, and the company suffered heavy losses.

Mostek's DRAM legacy is exemplified in the MK4116, MK4164 and MK41256, each of which were successfully cloned by competitors, both USA-based and overseas-based. "By four" DRAM was a simple adaptation of the MK4116/MK4164/MK41256 technology, utilizing a larger package to accommodate the additional data bits and multiplexing the data in/out pins as well; the basic *RAS, *CAS, *WRITE and multiplexed address bus concept was retained intact.

World leader in telecommunications products[edit]

Mostek enjoyed many years of mastery of the international market for telecommunications products. Their product line included telephone tone and pulse dialers, touchtone decoders, counters, top-octave generators (used by Hammond, Baldwin, and others), CODECs, watch circuits, and a host of custom products for a variety of customers. The products used the simple aluminum-gate PMOS (& later CMOS) process and helped maintain Mostek's cash flow through intense DRAM competition, and other semiconductor market pressures. In 1975 a smoky fire in the wafer fab fire closed it for several months and production of some critical products was shifted to a friendly fab in Silicon Valley.

Several employees played a key role in the Telecommunications and Industrial Products Department. Bob Paluck headed the department, assisted by Mike Callahan, Charles Johnson, William Bradley, Robert C. Jones, Bob Banks, Ted Lewis, Darin Kincaid, William Cummings, and a host of other employees. Lewis and Bradley were designated as key employees after the United Technologies purchase.

Bradley designed all of the custom products based on the single-chip-calculator platform, as well as the code for the wristwatch chips produced by Mostek for Bulova and other customers. For a short while, Paluck headed a joint venture called Mostek Hong Kong, a collaboration with Bulova for the production of high-end wristwatches based on Mostek designs. Bradley was an employee of that joint venture. Paluck left Mostek to work with Sevin Rosen Funds and Convex Computer. As Mostek's focus was shifted to its DRAM products, the industrial and telecommunications products were ignored and their market share vanished.

Microprocessor second sourcing deals[edit]

Mostek MK3880P (Zilog Z80).
Mostek MK3880 with metal
- metal layer
Mostek MK3880 without metal
- silicon only
Mostek MK3880 (Zilog Z80) die

With this foundation in calculator chips and high volume DRAM production, Mostek gained a reputation as a leading semiconductor "fabrication house" (fab) in the early 1970s.

In 1974 Mostek introduced the MK5065, an 8-bit PMOS microprocessor, with 51 instructions whose execution times range from 3 to 16 μs. Architectural features included multiple nested indirect addressing and three register sets (each consisting of an accumulator, a program counter and a carry/link bit) which could be used for interrupt processing or for subroutines.[2][3][4] Bill Mensch was one of the engineers who had actually designed the 5065 at Motorola for Olivetti.[5] A more popular product was the MK3870, which combined the two-chip Fairchild F8 (3850 + 3851) into a single chip, introduced in 1977. William Bradley designed a host of custom products based on the 3870. Fairchild later licensed the 3870 back from Mostek. Mostek also produced ROM chips on demand, as well as the chips powering the Hammond electronic organ.

During the introduction of the Z80, Zilog needed a production partner while they got their own fabs set up. They first signed a production agreement with Synertek, but the company later demanded they sign a second source agreement, allowing Synertek to produce and sell the design on their own. Zilog couldn't afford to do this before their own fabs were ready to compete, so the agreement was broken. They then selected Mostek as they were the only other company with a line capable of building a +5V device (as opposed to +5 and +12).[6] As they began work with Mostek they learned the company had developed advanced layout methods which they then applied to the Z80, resulting in the device being shrunk by 20%[7] Once their lines were set up, Mostek was able to sign a second source arrangement for what they called the MK3880.[8] The Z80 eventually became the most popular microcomputer family, and was used in millions of embedded devices as well as in many home computers and computers using the de facto standard CP/M operating system, such as the Osborne, Kaypro, and TRS-80 models.[a]

Mostek sought new microprocessor partners and negotiated deals with Intel to gain second sourcing rights to the Intel 8086 microprocessor family and future x86 designs and with Motorola for rights to the Motorola 68000 and VME. Mostek thus had secured the rights to every microprocessor family that would be important for the next 25 years. The Intel x86 microprocessors would go on to become the brains for the IBM PC, while the Motorola 68000 would become the heart of the Apple Macintosh line. However, as with its telecomm business, Mostek chose not to aggressively follow-up its entry into microprocessors—instead increasing its concentration on the highly competitive (and eventually unprofitable) DRAM business.

Decline in the face of Asian competition[edit]

Mostek was bought by United Technologies (UTC) in 1979 for US$345M to prevent an unfriendly takeover from Gould at the 10th anniversary of the company's founding, when a large block of stock options controlled by Sprague Electric became vested. UTC would go on to lose their investment. The leadership chosen for the semiconductor division did not appreciate the up-front investment required or the long time for ROI.[9] UTC sacrificed Mostek's leadership position in some markets, focusing on the DRAM basket. UTC at first invested hundreds of millions to expand Mostek, then hundreds of millions more trying to keep the company going during the various semiconductor and videogame crashes of the early 1980s, and eventually gave up in the fall of 1985, closed Mostek completely, and then sold it to the French Thomson Semiconductor for a mere $71 million.[10]

Unfortunately the DRAM marketplace was the beachhead where Japanese firms would make their successful assault on the global semiconductor market. Mostek was unable to match the Japanese extremely aggressive pricing, and succumbed during a particularly brutal price war when Korean firms (including Samsung, now the world's largest electronics conglomerate) tried to beat the Japanese at their own game. Micron Technology (one of several Mostek spinoffs) would later bring suit to prove the Japanese memory manufacturers guilty of price dumping, but the ruling would be too late to save Mostek.

Thomson called back only about 20% of the workforce in an attempt to return Mostek to profitability. The next year they merged Mostek with the Italian SGS-ATES to become STMicroelectronics, based in Geneva, Switzerland. Although by this time most of Mostek's designs were no longer commercially viable, their DRAM patents turned out to be valuable and STM started a series of lawsuits to collect royalties. Between 1987 and 1993 STM made $450 million on these licenses alone.[citation needed]


Jerry Rogers founded Cyrix in 1988 to capitalize on the Mostek second source agreement that allowed any 80X86 processor to be legally copied, which Intel attempted to stop via lawsuits. Eventually, after losing many legal battles, Intel simply changed the name of the 80586 to the Pentium, thereby ending the agreement.

Micron Technology was a very successful spinoff founded by a handful of Mostek employees, including Ward Parkinson, Dennis Wilson, and Doug Pitman.[citation needed]

Sevin Rosen Funds co-founded by LJ Sevin funded Compaq Computers, Cyrix, Convex Computers and more.[citation needed]

Bob Paluck started Convex Computers in ca 1979. Vin Prothro started Dallas Semiconductor in ca 1984. Mike Callahan started Crystal Semiconductor in ca 1979. Charles Johnson started SRX in ca 1981.


  1. ^ Older note left in: Mostek supposedly discovered that Zilog had modified the recipe for Z80 chips to keep the yields low[citation needed], thereby buying Zilog time to build their own fabs.


  1. ^ "Mostek 5065's by the 1000's" (PDF). Microcomputer Digest. Microcomputer Associates Inc. 8 (8): 1–2. February 1975. Retrieved 10 January 2021.
  2. ^ Integrated Circuit Guide. Mostek. 1974. pp. 78–80. Retrieved 2021-11-04.
  3. ^ Mostek 5065 instruction set: Billy Don Russel, Jr. (1975). A Microcomputer Based Substation Control System (PDF). University of Oklahoma. pp. 108–112. Retrieved 2021-11-04.
  4. ^ Banu John (2017-11-22). "The Western Design Center: Guiding The Past, Present And Future Of Microprocessor Technology". Embedded Advisor. Retrieved 2021-11-04.
  5. ^ Slater 2007, p. 7.
  6. ^ Slater 2007, p. 11.
  7. ^ Slater 2007, p. 4.
  8. ^ Proebsting, Robert. "Oral History of Robert Proebsting" (PDF). Computer History Museum. Retrieved 13 June 2014.
  9. ^ "Sale of Mostek Is Completed". New York Times. November 14, 1985. p. D.4. The United Technologies Corporation said yesterday that it had completed the sale of its financially troubled Mostek semiconductor subsidiary to Thomson-CSF, a French Government electronics company, for about $71 million.

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