He is a co-founder, the former chairman, and the former chief scientist of Rambus Inc.. Horowitz has authored over 700 published conference and research papers and is among the most highly-cited computer architects of all time.

At Stanford his research focused on VLSI circuits[8] and he led a number of early RISC processor designs, including MIPS-X.

He has worked on RISC processors, multiprocessor designs, low-power circuits, high-speed links, computational photography, and genomics.

[16] In 2007, he was elected to the National Academy of Engineering for his "leadership in high-bandwidth memory-interface technology and in scalable cache-coherent multiprocessor architectures.

[10] At the 2014 International Solid-State Circuits Conference, he presented his studies on the outlook for the semiconductor industry in Computing's Energy Problem (And What We Can Do About It).

[8][17][20] Horowitz returned briefly to Rambus in 2005 to help start a research organization at the company and left the board of directors in 2011.