To provide a manufacturing method of a highly reliable TFT, by which a more refined pattern can be formed through a process using four or three masks, and a semiconductor device. A channel-etched bottom gate TFT structure is adopted in which a photoresist is selectively exposed to light by rear surface exposure utilizing a gate wiring to form a desirably patterned photoresist, and further, a halftone mask or a gray-tone mask is used as a multi-tone mask. Further, a step of lifting off using a halftone mask or a gray-tone mask and a step of reflowing a photoresist are used.