Stacked-device power combining method can simultaneously increase output power and load impedance by raising the bias voltage of the overall circuit. The series-input and series-output configuration is physically realizable for multicell stacked device configuration in monolithic circuits. To prove this concept, a 4-cell stacked power amplifier with series-input and series-output configuration is demonstrated in this paper using 2 μm HBT. Almost no additional matching is required to achieve power match and good return loss. The amplifier shows a measured performance of 14 dB gain at 5 GHz, P1db of 26 dBm and saturation power of 1 W at 4.8 GHz. This is the first demonstration of a fully monolithic 4 cell series stacked amplifier. The ease of design and its overall simplicity suggests that this method can be carried out in many other power applications.