A method for manufacturing a semiconductor device having favorable electric characteristics with high productivity is provided. A first microcrystalline semiconductor film is formed over an oxide insulating film under a first condition that mixed phase grains with high crystallinity are formed at a low particle density. After that, a second microcrystalline semiconductor film is stacked over the first microcrystalline semiconductor film under a second condition that a space between the mixed phase grains are filled by the crystal growth of the mixed phase grains of the first microcrystalline semiconductor film.