Fabrication methods for integrating CMOS and BJT devices are presented. A semiconductor substrate having a first region and a second region are provided, wherein the first region includes a CMOS device, and the second region includes a BJT device. A dielectric layer is conformably deposited on the semiconductor substrate. Part of the dielectric layer is removed, thereby forming sidewall spacers on a gate structure of the CMOS device and remaining a thin dielectric layer on the BJT device. The remaining thin dielectric layer is completely removed, completing integration of the CMOS device and the BJT device.