The article investigates the temperature dependences of the current–voltage characteristics and reverse recovery of high-voltage AlxGa1–xAs and AlxGa1–xAs1–ySby p–i–n diodes manufactured by liquid-phase epitaxy when heated to 350 °C. It was found that with an increase in the Al content in the base layers, the operating temperatures of the diodes increase from 250 °C at x = 0 to 350 °C at x ~ 0.45, while the forward voltage drops of the diodes also increase. It is shown that the use of small Sb additions in AlGaAs layers reduces the reverse recovery times of diodes by almost an order of magnitude, from 40–80 ns to 5–8 ns.