Roku has tripled in value this year, outperforming almost every notable technology stock, and Kyle Evans of investment bank Stephens says the rally has finally gone too far.

Evans downgraded his rating on Roku to "equalweight" from "overweight," citing too much near-term risk to the stock after the run-up that pushed the streaming video company to a market cap of about $11 billion. The analyst pointed to last year's third-quarter results and Roku's slight miss in platform revenue, which sent the stock down 22%.

The shares dropped 7.3 to $88.83 on Tuesday.