In 1979, soon after its market peak, Mostek was purchased by United Technologies Corporation for $345M. In 1985, after several years of red ink and declining market share, UTC sold Mostek for $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.
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 shifter chip. This was followed by a 1k PMOS aluminum-gate 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 a tremendous gain in the control of doping profiles. 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. Hewlett-Packard also contracted with Mostek for mask development and production of chips for their HP-35 and HP-45 lines.
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 64Kb 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)