A semiconductor device including an oxide semiconductor and an organic resin film is manufactured in the following manner. Heat treatment is performed on a first substrate provided with an organic resin film over a transistor including an oxide semiconductor in a reduced pressure atmosphere; handling of the first substrate is performed in an atmosphere containing moisture as little as possible in an inert gas (e.g., nitrogen) atmosphere with a dew point of lower than or equal to −60° C., preferably with a dew point of lower than or equal to −75° C. without exposing the first substrate after the heat treatment to the air; and then, the first substrate is bonded to a second substrate that serves as an opposite substrate.