Low-temperature-grown GaAs buffers are incorporated into pseudomorphic high-electron-mobility transistors in order to improve channel breakdown. X-ray diffraction measurements are used to determine the reproducibility of arsenic incorporation into low-temperature-grown GaAs layers. Hall measurement results from pseudomorphic high-electron-mobility transistors structures show little reduction in channel electron mobility and sheet density when the spacer between the low-temperature-grown buffer and the channel is greater than similar to 90 nm. Pseudomorphic high-electron-mobility transistors devices using the improved buffer have shown a 45% increase in channel breakdown voltage, a 12% increase in rf power output, and an 8% increase in power-added efficiency at 20 GHz when contrasted with the conventional-buffered pseudomorphic high-electron-mobility transistors.