A method of fabrication a transistor device with a non-uniform stress layer including the following processes. First, a semiconductor substrate having a first transistor region is provided. A low temperature deposition process is carried out to form a first tensile stress layer on a transistor within the first transistor region, wherein a temperature of the low temperature deposition process is lower than 300 degree Celsius (° C.). Then, a high temperature annealing process is performed, wherein a temperature of the high temperature annealing process is at least 150° C. higher than a temperature of the low temperature deposition process. Finally, a second tensile stress layer is formed on the first tensile stress layer, wherein the first tensile stress layer has a tensile stress lower than a tensile stress of the second tensile stress layer.