Single-walled carbon nanotubes (SWNTs) possess superior electronic and physical properties that make them ideal candidates for making next-generation electronic circuits that break the size limitation of current silicon-based technology(1-4). The first critical step in making a full SWNT electronic circuit is to make SWNT intramolecular junctions in a controlled manner. Although SWNT intramolecular junctions have been grown by several methods(2,5-8), they only grew inadvertently in most cases. Here, we report well-controlled temperature-mediated growth of intramolecular junctions in SWNTs. Specifically, by changing the temperature during growth, we found that SWNTs systematically form intramolecular junctions. This was achieved by a consistent variation in the SWNT diameter and chirality with changing growth temperature even though the catalyst particles remained the same. These findings provide a potential approach for growing SWNT intramolecular junctions at desired locations, sizes and orientations, which are important for making SWNT electronic circuits.