He was a major contributor to the design of the Motorola 6800 8-bit microprocessor and was part of the team led by Chuck Peddle that created the MOS Technology 6502.

[1] Mensch is the founder, chairman, and chief executive officer (CEO) of the Western Design Center (WDC) located in Mesa, Arizona.

He has taught classes at Arizona State University, including courses on system on chip (SoC) integrated circuit (IC) design.

[2] Based on his participation in the basic circuit design, definition, and system design of the Motorola 6800 microprocessor and supporting computer chips, Mensch is a co-holder of several 6800 family patents, including the 6800 central processing unit (CPU), 6820/21 Peripheral Interface Adapter (PIA), 6850 Asynchronous Communications Interface Adapter (ACIA), and 6860 modem chip.

Shortly after Mensch founded the Western Design Center (WDC) in 1978, Commodore International contracted the company to develop what they called a "macro-micro", a macro-programmed complementary metal–oxide–semiconductor (CMOS) processor that could be used in a small and powerful calculator.

[5] Mensch claimed that Commodore never intended to use his design, and were instead seeking leverage to get a better deal for competing chips from Japanese producer Toshiba.

The 65C02, in addition to being implemented in CMOS circuit technology that reduced power use and improved noise immunity, added some new instructions, and corrected several defects in the NMOS 6502.