Seahawks quarterback Geno Smith -- who started three games for Seattle this season -- was arrested early Monday morning on suspicion of DUI in Washington ... TMZ Sports has confirmed.
A spokesperson for the Washington State Patrol tells us ... Smith was pulled over at around 2 a.m. in King County -- just hours after the Seahawks returned home from beating the Cardinals in Arizona on Sunday.
According to law enforcement, Smith was initially stopped for speeding ... and was booked into the King County Jail a short time later.