A method for fabricating strained silicon transistors is disclosed. First, a semiconductor substrate is provided, in which the semiconductor substrate includes a gate, at least a spacer, and a source/drain region formed thereon. Next, a precursor, silane, and ammonia are injected, in which the precursor is reacted with silane and ammonia to form a high compressive stress film on the surface of the gate, the spacer, and the source/drain region. Preferably, the high compressive stress film can be utilized in the fabrication of a poly stressor, a contact etch stop layer, and dual contact etch stop layers.