(Adds Watermark in second paragraph; switches passive sentence to active in fifth paragraph)
By Sarah McBride
SAN FRANCISCO, Nov 17 (Reuters) - Gender diversity in the San Francisco Bay Area technology sector has improved over the last five years, but the region's most gender-diverse businesses are in the retail, biopharmaceuticals and financial services sector, a new study from the University of California, Davis, found.
Out of the 223 largest publicly traded companies headquartered in the Bay Area, more than one third had either zero or just one top position held by a woman, according to the study, in which executive women's group Watermark was a partner.
Still, that represents a big improvement from five years ago, when almost two-thirds of Bay Area companies had either zero or one top position held by a woman.
Retailer Williams-Sonoma, biopharmaceutical company Medivation and bank Wells Fargo ranked as the companies with the most high-ranking positions held by women, researchers said. In the technology sector, the most diverse player was software company Zendesk, tied for No. 4. Search engine Yahoo, led by Chief Executive Marissa Mayer, tied for No. 8.
The results come as major companies make public efforts to hire more women and ethnic minorities. In particular, the lack of diversity at Silicon Valley's technology companies has drawn national criticism.
The study defined top position as either a company board member or an executive whose compensation was high enough to be disclosed to the U.S. Securities and Exchange Commission.
Those with no women in a top position included network security company Palo Alto Networks, data company Hortonworks and Cypress Semiconductor.
Ingrid Burton, Hortonworks' recently appointed chief marketing officer, said diversity was a "top priority" at the company.
Representatives of other companies said restricting the pool to only those executives with SEC-reported compensation was too narrow.
Software companies had one of the highest percentages of women directors and the lowest of top-paid executives, said study author Amanda Kimball.
Starting last year, many top Bay Area tech companies began releasing diversity statistics, generally reporting around one quarter of their top employees were women.
In the UC Davis study, iPhone maker Apple ranked No. 25, social network Facebook No. 30 and search engine Google No. 68 among Bay Area companies on gender diversity.
Chipmaker Intel, which at the start of the year said it would spend $300 million over five years to improve diversity, ranked No. 48. Networking company Cisco Systems , which started releasing diversity figures a decade ago, ranked No. 41.
Reporting by Sarah McBride; Editing by Leslie Adler and Alan Crosby