There is provided a method in which a TFT with superior electrical characteristics is manufactured and a high performance semiconductor device is realized by assembling a circuit with the TFT. The method of manufacturing the semiconductor device includes: a step of forming a crystal-containing semiconductor film by carrying out a thermal annealing to a semiconductor film; a step of carrying out an oxidizing treatment to the crystal-containing semiconductor film; a step of carrying out a laser annealing treatment to the crystal-containing semiconductor film after the oxidizing treatment has been carried out; and a step of carrying out a furnace annealing treatment to the crystal-containing semiconductor film after the laser annealing. The laser annealing treatment is carried out with an energy density of 250 to 5000 mJ/cm.sup.2.