The Scot's dismissal comes just 16 months after his appointment, and just hours after a 2-0 friendly win over China.
The 59-year-old from Glasgow departs despite the United States fending off Germany to remain the world's best women's team in the latest Fifa rankings. The Americans won 18 of his 24 games in charge and suffered only two defeats, but significantly both of these came last month against Sweden and Denmark in the Algarve Cup.
Sermanni, whose first game was a 4-1 friendly win over Scotland in February 2013, said of the sacking: "I'll be honest, it came as a surprise to me. I didn't perceive that there were issues and I didn't feel that within the playing group. I didn't sense the players weren't on board with the direction we were trying to go in, but perhaps I was wrong. I honestly thought in the Algarve Cup that we had one of those tournaments where things didn't go right results-wise, but the performances were promising and showed we were actually going in the right direction.
"I feel incredibly privileged to have been in this position and a little disappointed and sad that I'm not able to continue and finish the job. I wouldn't have taken it on if I didn't want to see it through to the conclusion."
Scotland's under-19 women, meanwhile, are poised to become the third national side to reach a Uefa European Championship finals in 12 months. Gareth Evans' side beat hosts Croatia 2-0 yesterday. They beat Iceland 5-1 in their opening Group 2 match on Saturday and a draw with Russia on Thursday will be enough to see them through to July's finals in Norway.