A power amplifier according to some embodiments includes a submount, a monolithic microwave integrated circuit (MMIC) die on the submount, the MMIC die including an RF transistor configured to operate at frequencies greater than 26.5 GHz, and an internal decoupling capacitor on the submount and connected to a drain of the RF transistor. The internal decoupling capacitor has a capacitance greater than 2 nF.