The present invention discloses a method for manufacturing a semiconductor device, comprising: forming an insulating isolation layer on a substrate; forming an insulating isolation layer trench in the insulating isolation layer; forming an active region layer in the insulating isolation layer trench; forming a semiconductor device structure in and above the active region layer; characterized in that the carrier mobility of the active region layer is higher than that of the substrate. Said active region is formed of a material different from that of the substrate, the carrier mobility in the channel region is enhanced, thereby the device response speed is improved and the device performance is enhanced. Unlike the existing STI manufacturing process, for the present invention, an STI is formed first, and then filling is performed to form an active region, thus avoiding the problem of generation of holes in STI, and improving the device reliability.