Using advanced epitaxy and process technologies, we fabricated a planar-doped AlGaAs/GaAs HEMT with gates 0.1 micrometers long. At 12 GHz, the device had a noise figure (NF), including the package loss, of 0.50 dB with an associated gain (Gas) of 13.0 dB. This is, to our knowledge, the lowest NF at 12 GHz reported for AlGaAs/GaAs HEMTs. For GaAs-based InGaP/InGaAs HEMTs, we obtained a NF, including the package loss, of 0.41 dB at 12 GHz with a Gas of 13.0 dB, and a NF of 1.2 dB at 50 GHz with a Gas of 5.8 dB. These high-performance GaAs- based HEMTs are widely used at microwave frequencies. Millimeter wave applications also require low-cost high-performance HEMTs.