A method for manufacturing a thin film transistor including a step of forming a polymer film (a) to a layer above a support substrate, a step of forming a semiconductor element above the polymer film (a), and a step of separating the support substrate from the polymer film (a) formed with the semiconductor element in which the polymer film (a) has a thickness of 1 μm or more and 30 μm or less, a transmittance of 80% or higher to a visible light at a wavelength of 400 nm or more and 800 nm or less, a 3 wt % loss temperature of 300° C. or higher, and a melting point of 280° C. or higher.