Affymetrix, Inc. was an American company that manufactured DNA microarrays; it was based in Santa Clara, California, United States. The company was acquired by Thermo Fisher Scientific in March 2016.

The company was founded by Dr. Stephen Fodor in 1992. It began as a unit in Affymax N.V. in 1991 by Fodor's group, which had in the late 1980s developed methods for fabricating DNA microarrays, called "GeneChip" according to the Affymetrix trademark, using semiconductor manufacturing techniques. The company's first product, an HIV genotyping GeneChip, was introduced in 1994 and the company went public in 1996. As a result of its pioneering work and the ensuing popularity of microarray products, Affymetrix derived significant benefit from its patent portfolio in this area.

Affymetrix acquired Genetic MicroSystems for slide-based microarrays and scanners, Neomorphic for bioinformatics, ParAllele Bioscience for custom SNP genotyping, USB/Anatrace for biochemical reagents, eBioscience for flow cytometry, and Panomics and True Materials to expand its offering of low to mid-plex applications. In 2000, Perlegen Sciences spun out from Affymetrix to focus on wafer-scale genomics for massive data creation and collection required for characterizing population variance of genomic markers and expression for the drug discovery process.

On January 8, 2016, Thermo Fisher Scientific announced the acquisition of Affymetrix for approximately $1.3 billion. The acquisition closed on March 31, 2016.

Affymetrix makes quartz chips for analysis of DNA Microarrays called GeneChip arrays. Affymetrix's GeneChip arrays assist researchers in quickly scanning for the presence of particular genes in a biological sample. Within this area, Affymetrix is focused on oligonucleotide microarrays. These microarrays are used to determine which genes exist in a sample by detecting specific pieces of mRNA. A single chip can be used to analyze thousands of genes in one assay. Chips can be used only once.

Affymetrix sells both mass-produced GeneChip arrays intended to match scientifically important parts of human and other animal genomes. Affymetrix manufactures its GeneChip arrays using photolithography. The company also manufactures machinery for high speed analysis of biological samples.

Affymetrix GeneChip Operating Software is a software system for managing Affymetrix microarray data.

Competitors in the DNA Microarray business include Illumina, GE Healthcare, Applied Biosystems, Beckman Coulter, Eppendorf Biochip Systems [1], and Agilent. There are also various inexpensive plastic-based technologies under development in small companies and laboratories around the world. It has been widely speculated that mass-produced plastic chips can be produced at lower prices than Affymetrix's quartz chips.

The Food and Drug Administration in January 2014 cleared a first-of-a-kind whole-genome postnatal blood test that can aid physicians in identifying the underlying genetic cause of developmental delay, intellectual disability, congenital anomalies, or dysmorphic features in children. This test, known as CytoScan Dx Assay, is designed to diagnose these disabilities earlier to expedite appropriate care and support. "About 2 to 3 percent of U.S. children have some sort of intellectual disability, according to the National Institutes of Health."