The invention provides a manufacturing method of an amorphous silicon membrane and a semiconductor device. In the manufacturing method of the amorphous silicon membrane, a two-step membrane forming technology is adopted; in a first-step membrane forming stage, a first amorphous silicon layer with small deposition crystalline grains and high uniformity is deposited in an atomic layer deposition mode; in a second-step membrane forming stage, a second amorphous silicon layer doped with carbon atoms or nitrogen atoms is deposited on the first amorphous layer; carbon atoms or nitrogen atoms are doped in crystal lattices of the second amorphous silicon layer; and silicon atoms can be prevented from being continuously deposited on silicon crystalline grains of the first amorphous silicon layer, so that an amorphous silicon membrane with a small grain size is obtained. Moreover, in the manufacturing method of the semiconductor device, amorphous silicon with small grain size is obtained by the manufacturing method of the amorphous silicon membrane so as to meet requirements of performance of the device, particularly, after the amorphous silicon with the small grain size serves as a virtual amorphous silicon grid electrode, a groove with smooth side walls can be formed after the amorphous silicon with the small grain size is removed, the deposition morphology of a follow-up metal grid is improved, and the electric leakage performance is improved.