Si1-xGex low temperature selective epitaxial growth was investigated by using a UHV/CVD system with high pressure H-2 pre-cleaning of the substrate and SiGe HBTs were fabricated. The selective epitaxial growth was achieved by using different incubation times for Si(100) substrate and mask layers. Device performances show the good crystallinity of selectively grown Si1-xGex layer: an extremely high current gain of 45 000 and a high cutoff frequency of 154 GHz were achieved in the HBT with a maximum Ge content of 25%. Furthermore, the comparison of AC performance between self-aligned and non-self-aligned transistors demonstrates the advantage of the self-aligned structure formed by the Si1-xGex low-temperature selective epitaxial growth.