Five of the 10 most expensive office markets in the U.S. are tech hubs, with Main Street in Cambridge’s Kendall Square now commanding the nation’s fourth-highest rents at nearly $90 per square foot.

JLL’s 2017 “Most Expensive Streets” report pegs Silicon Valley’s Sand Hill Road venture capital mecca as the priciest office space in the U.S., with average full-service rents in the third quarter approaching $120 per square foot. New York’s Fifth Avenue and Mission Street in San Francisco rounded out the top three.

Life science hotspot Kendall Square is fetching the nation’s highest rent premiums compared with the regional market, with tenants paying full-service rents of $90 per square foot, or 144 percent more than the average in Greater Boston.

Cambridge’s sky-high rents are influencing the office market in Boston, particularly in Back Bay which is traditionally the city’s highest-cost submarket. Boylston Street ranked eighth in this year’s survey, down a notch from 2016, but still attaining full-service rents of nearly $69 per square foot.

“We have seen a shift in tenancy and more migration between Cambridge and Boston,” JLL Managing Director Frank Petz said in a statement. “The proliferation of life science players in Cambridge has dislodged many traditional office users and even tech companies. Boston is benefiting as tech tenants cross the river to take advantage of the value proposition the city offers.”